Modifications by est31: grammar fixes in doc + error messages and
a little style fix, no functional change.

This commit refactors the majority of the Mapgen settings system.
- MapgenParams is now owned by MapSettingsManager, itself a part of ServerMap,
  instead of the EmergeManager.
- New Script API functions added:
    core.get_mapgen_setting
    core.get_mapgen_setting_noiseparams,
    core.set_mapgen_setting, and
    core.set_mapgen_setting_noiseparams.
- minetest.get/set_mapgen_params are deprecated by the above new functions.
- It is now possible to view and modify any arbitrary mapgen setting from a mod,
  rather than the base MapgenParams structure.
- MapgenSpecificParams has been removed.

- Move mapgen creation logic out of EmergeManager and into Mapgen
- Internally represent mapgen type as an enum value, instead of a string
- Remove the need for a MapgenFactory per mapgen

Deprecate get_look / set_look pitch / yaw

Mgvalleys: Remove riverbed sand placement from base terrain generation
Riverbed material placement moved to MapgenBasic::generateBiomes()
Document fields and add note that the biome API is still unstable

This fixes value truncation (and therefore incompatibility) on platforms
with an LP32 data model, such as VAX or MS-DOS.

Gives a convenient way to check a player's password.

This entirely bypasses the SRP protocol, so should be used
with great care.

This function is not intended to be used
in-game, but solely by external protocols, where no
authentication of the minetest engine is provided, and
also only for protocols, in which the user already gives the
server the plaintext password.

Examples for good use are the classical http form, or irc,
an example for a bad use is a password change dialog inside
formspec.

Users should be aware that they lose the advantages of the SRP
protocol if they enter their passwords for servers outside the
normal entry box, like in in-game formspec menus,
or through irc /msg s,

This patch also fixes an auth.h mistake which has mixed up the
order of params inside the decode_srp_verifier_and_salt function.

Zeno-: Added errorstream message for invalid format when I committed

Note that the macro CHECK_FILE_ERR implements the code removed

Adds the particle option `collision_removal = bool`

Some particles are hard to use right now since they either go through
solid blocks (without collision detection), and with collision
detection enabled they (e.g. raindrops) would just stop dead on the
floor and sit there until they expire, or worse, scrape along a wall
or ceiling.

We can solve the problem by adding a boolean flag that tells the
particle to be removed if it ever collides with something. This will
make it easier to add rain that doesn't fall through your roof or stick
on the top of it. Or clouds and smoke that don't go through trees.

Particles that collide with this flag are marked expired
unconditionally, causing them to be treated like normal expired
particles and cleaned up normally.

Documentation is adjusted accordingly.

An added bonus of this patch is that particles can potentially collide
many times with nodes, and this reduces the amount of collisions to 1
(max), which may end up reducing particle load on the client.

BiomeGen defines an interface that, given a set of BiomeParams, computes biomes
for a given area using the algorithm implemented by that specific BiomeGen.
This abstracts away the old system where each mapgen supplied the noises
required for biome generation.

* Fix naming style for methods and classes:
	Use camelCase for methods and PascalCase for classes as
	code style demands it. And use sneak_case for methods that
	are not member of a class.
* Replace "* " with " *" for Pointers
* Same for references
* Put function body opening braces on new line
* Other misc minor non functional style improvements

The legacy init packet (pre v25) sends information about the client's
password that a server could use to log in to other servers if the
username and password are the same. All the other benefits of SRP of
protocol v25 are missed if the legacy init packet is still sent during
connection creation.

This patch adds an option to not send the v25 init packet. Not sending
the v25 packet means breaking compat with pre v25 servers, but as the
option is not enabled by default, no servers are affected unless the
user explicitly flips the switch. More than 90% of the servers on the
serverlist support post v25 protocols.

The patch also fixes a bug with greying out of non compliant servers
being done wrongly, the min and max params were mixed.

* No function overloading
* Adhere coding style and with method names following
  lowercase_underscore_style
* Use std::string in external API, handling these is
  much more fun

NDT_CONNECTED attempts to connect to any side of nodes that it can
connect to, which is troublesome for FACEDIR type nodes that generally
may only have one usable face, and can be rotated.

We introduce a node parameter `connect_sides` that is valid for
any node type. If specified, it lists faces of the node (in "top",
"bottom", "front", "left", "back", "right", form, as array) that
connecting nodeboxes can connect to. "front" corresponds to the south
facing side of a node with facedir = 0.

If the node is rotatable using *simple* FACEDIR, then the attached
face is properly rotated before checking. This allows e.g. a chest
to be attached to only from the rear side.

We introduce a new nodebox type "connected", and allow these nodes to
have optional nodeboxes that connect it to other connecting nodeboxes.

This is all done at scenedraw time in the client. The client will
inspect the surrounding nodes and if they are to be connected to,
it will draw the appropriate connecting nodeboxes to make those
connections.

In the node_box definition, we have to specify separate nodeboxes for
each valid connection. This allows us to make nodes that connect only
horizontally (the common case) by providing optional nodeboxes for +x,
-x, +z, -z directions. Or this allows us to make wires that can connect
up and down, by providing nodeboxes that connect it up and down (+y,
-y) as well.

The optional nodeboxes can be arrays. They are named "connect_top,
"connect_bottom", "connect_front", "connect_left", "connect_back" and
"connect_right". Here, "front" means the south facing side of the node
that has facedir = 0.

Additionally, a "fixed" nodebox list present will always be drawn,
so one can make a central post, for instance. This "fixed" nodebox
can be omitted, or it can be an array of nodeboxes.

Collision boxes are also updated in exactly the same fashion, which
allows you to walk over the upper extremities of the individual
node boxes, or stand really close to them. You can also walk up
node noxes that are small in height, all as expected, and unlike the
NDT_FENCELIKE nodes.

I've posted a screenshot demonstrating the flexibility at
    http://i.imgur.com/zaJq8jo.png
In the screenshot, all connecting nodes are of this new subtype.

Transparent textures render incorrectly, Which I don't think is
related to this text, as other nodeboxes also have issues with this.

A protocol bump is performed in order to be able to send older clients
a nodeblock that is usable for them. In order to avoid abuse of users
we send older clients a "full-size" node, so that it's impossible for
them to try and walk through a fence or wall that's created in this
fashion. This was tested with a pre-bump client connected against a
server running the new protocol.

These nodes connect to other nodes, and you can select which ones
those are by specifying node names (or group names) in the
connects_to string array:
      connects_to = { "group:fence", "default:wood" }
By default, nodes do not connect to anything, allowing you to create
nodes that always have to be paired in order to connect. lua_api.txt
is updated to reflect the extension to the node_box API.

Example lua code needed to generate these nodes can be found here:
    https://gist.github.com/sofar/b381c8c192c8e53e6062

I've written several experimental bits of code that revolve around the
need for a consistent calendar, but implementing one is extremely hard
in mods due to time changes and mods overriding core.get_timeofday(),
which will conflict.

The second part of the problem is that doing this from a mod requires
constant maintenance of a settings file.

An implementation in core is trivial, however, and solves all of
these problems at virtually no cost: No extra branches in server
steps, and a single branch when minetest.set_time_of_day(), which is
entirely reasonable.

We store the day_count value in env_meta.txt.

The use case is obvious: This change allows mods to create an actual
virtual calendar, or properly account for seasonal changes, etc..

We add a "/days" chatcommand that displays the current day count. No
permissions are needed. It can only retrieve the day count, not
modify it.

* Replace string by-val passing with const reference
* Fix code style
* Remove redundant `int table` definition and indentation level

Throwing a LuaError calls destructors as it propagates up the stack,
wheres lua_error just executes a longjmp.

Fixes #3764

This function could be used to steal insecure environments from trusted mods.

Fixes #3765

This allows mods to perform both asynchronous and synchronous HTTP
requests. Mods are only granted access to HTTP APIs if either mod
security is disabled or if they are whitelisted in any of the
the secure.http_mods and secure.trusted_mods settings.

Adds httpfetch_caller_alloc_secure to generate random, non-predictable
caller IDs so that lua mods cannot spy on each others HTTP queries.

Previously you could steal a secure environment from a trusted mod by wrapping
request_insecure_environment with some code like this:

local rie_cp = minetest.request_insecure_environment
local stolen_ie
function minetest.request_insecure_environment()
	local ie = rie_cp()
	stolen_ie = stolen_ie or ie
	return ie
end

* Sky: rename Box => m_box and inline getBoundingBox
* Uniformize aabbox3d<f32> to aabb3f

`errorstream` must not be overly verbose as clientside it is directly printed
onto the ingame chat window. These days, the serverlist can contain > 200k bytes,
so better print it to warningstream if the data buffer is too long.

Previous commits broke it... :(

Backface culling is enabled by default for all tiles, as this
is how the lua parser initializes each tiledef. We revert to
always using the value from the tiledef since it is always
read and serialized.

Mods that wish to enable culling for e.g. mesh nodes, now can
specify the following to enable backface culling:

    tiles = {{ name = "tex.png", backface_culling = true }},

Note the double '{' and use of 'name' key here! In the same
fashion, backface_culling can be disabled for any node now.

I've tested this against the new door models and this properly
allows me to disable culling per node. I've also tested this
against my crops mod which uses mesh nodes where culling needs
to be disabled, and tested also with plantlike drawtype nodes
where we want this to continue to be disabled.

No default setting has changed. The defaults are just migrated
from nodedef.cpp to c_content.cpp.