Major refactor of emerge.cpp and Map::init/finishBlockMake

It returns the index used in mg->biomemap for a given biome name.
The biomemap is useless without this unless you re-register all existing biomes,
which could cause problems for anyone else trying to use biomemap.
With this, you can quickly create a lookup table of ids and names.

Also add PATH_DELIM for Windows compatibility.

Get facedir by using lowest 5 bits of param2 and limiting to 23
More robust, frees up higher param2 bits for other uses
Change lookup table and table index to u8

-> Remove memory allocation bugs
-> Merge changes from upstream, enabling customizeable memory allocation

1. Check for entity addition success in spawn_item implementation
2. Check for success in item_drop callback, so that the player
doesn't lose the item if they are outside bounds and try to drop it.
3. When existing player joins game, check that their position is inside
map bounds. If not, set their position to the return value of findSpawnPos().
4. Make findSpawnPos() respect the border

2 fixes a lua crash if a player drops an item outside map bounds.
3 fixes an assertion crash if a player leaves when being outside map bounds,
and then rejoins.

Because the count is serialized as u16, this would cause overflow.

If minetest later deserialized a mapblock with an incorrect
static object count, it would be unable to find the NameIdMapping
(which comes after the StaticObjectList) and abort with an error
such as "Invalid block data in database: unsupported NameIdMapping
version" (issue #2610).

Sidelen larger than 16 is essential for low density decorations
With sidelen > 16 chunksize may not be divisable by sidelen if
chunksize is changed, in this situation setting sidelen = chunksize
is desirable and should not create error messages.

Change a remaining assert(0) call to FATAL_ERROR(msg).
There was a regression since commit

ced6d202 "For usages of assert() that are meant to persist in Release builds (when NDEBUG is defined), replace those usages with persistent alternatives"

where when an "uncatched" exception is thrown inside a "side thread",
the program doesn't abort anymore.

This led to the problem @netinetwalker experienced where the emergethread
got an unhandled exception for loading a mapblock while redis was loading,
(see #3196) and then jmped outside its loop to work down its queue.
This resulted in the server not doing any emerges anymore.

Thanks to @netinetwalker for spotting the error, proposing a fix, and testing it.

Error due to @est31's merging changes to PR #3202 to add more error reporting for invalid reply types, commit:

524a7656 "redis: throw error if block request failed"

Now we branch out on the valid reply type "not found".

On world load the collision code can not see node boxes, since the
nodes have not been loaded. Thus it collided only at the next full
node. However, standing on a slab on world load leaded to sinking into
it until the world finished loading. Then one maybe fell further, if
the node below was not walkable.

Now, with this commit, when no node around the player has been loaded
it simply does not move the player.

Fixes #3196. Before, we didn't throw an error, and the engine thought the
block isn't occupied. But in fact it might be that redis is still loading,
and the block does exist in the database. The result was a cheesy map.

Why doing things simple ? Use pointer instead of strings to save players and remove them.
Saving players by name does a lookup to find pointer we already have ! Idem with removePlayer
Also remove unused removePlayer(peer_id), it's never called

-> Don't pass pointer to whole IGameDef to NodeMetadata constructors
	and deserializers, but only to IItemDefManager, which is needed
-> Remove the unused content_mapnode_get_new_name() method
-> Fix style for MapBlock::deSerialize and MapBlock::deSerialize_pre22,
	improving accuracy of error messages a bit
-> Fix style at other serialisation methods too
-> Improve accuracy of some comments

Use std::queue instead of std::set, we don't need such a heavy container.
Don't convert position to int to convert it back to float in the next function.

The legacy code added in commit

d879a539 - "Add minetest.swap_node"

for sending the whole mapblock to older clients on the case of a node
modification with swap_node, had the problem that the block chosen to be
sent to the client was referenced with node coordinates and not with
block coordinates, resulting in getting the wrong block sent to the client.

Borders have to be converted into BS format in order to be accurately comparable to
object positions.

Entity positions are serialized as F1000. Disallow placing
entities outside safe borders with the minetest.add_entity
call.

Note that this patch only enforces those boundaries for
placing entities, moving entities that move outside boundaries
aren't affected.

Thanks to @nanepiwo for pointing this out.

Remove unusable fine rotation by param2
Remove unused and redundant code
Fix code style issues

1. Do two renames:
	* SER_FMT_CLIENT_VER_LOWEST -> SER_FMT_VER_LOWEST_WRITE
	* SER_FMT_VER_LOWEST -> SER_FMT_VER_LOWEST_READ
Now the two define values are consistently named with the _WRITE defines
SER_FMT_VER_{HIGHEST,LOWEST}_WRITE, and to better point out what the two
serialisation versions actually are for.

2. wrap some lines in doc/worldformat.txt, and point out that the node
timers are serialized at a later point, as this can cause confusion about
what now happens (if one doesn't strictly read the if block's conditions).

3. some whitespace fixes in NodeTimerList::serialize, and one new comment.

Modders are now able to select the range of ore column height,
and the midpoint at which they 'grow' starting from.
This commit adds three new parameters for the 'sheet' ore type:
column_height_min, column_height_max, and column_midpoint_factor.
clust_size is now deprecated for this ore type.

Its obvious that "u16 command" is inside every packet, therefore this
commit removes all mentions of the command, if non-array like notation
is used. We already didn't add "u16 command" to new packets or removed
it at packet changes, so now we remove it from existing packets.

Use in-place locale directory if that exists, and
static one (RUN_IN_PLACE or CUSTOM_LOCALEDIR) doesn't exist.
Report to errorstream if neither static nor in-place locale
dirs exist, and report successfully found paths to infostreem.

Fixes two bugs:

-> Regression of commit [1] where if we use RUN_IN_PLACE=false,
	but don't make install, locales aren't found. One might
	think this is no regression, as its no bug, but all other
	paths (mainmenu, etc.) are detected properly.
-> Regression of commit [1] where locales don't work on windows.

References:
[1]: Commit 645e2086 "Use CUSTOM_LOCALEDIR if specified" by @ShadowNinja

As indicated in its name, m_client_event_queue should be a queue.
Change std::list to std::queue to improve the queue's performance.

Commit

e4bff8be - Clean up threading

by @ShadowNinja has broken the OSX build.

Including things inside a namespace isn't good.

Also fixes #3124.

Before, calling get_areas_in_area for an areastore with both
include_borders and include_data would result in a lua error,
if there was at least one area as result:
attempt to index a number value in function 'get_areas_in_area'