This privilege allows map protection bypassing for server operators
and world moderators.

Initially I had thought that bypassing protection mods would have been
something that could entirely be done inside mods and minetest_game,
but the concept of protection is defined in core, in the code of
core.is_protected().

I don't feel that it would be logical to introduce a protection
concept in core, but not some way around that for server operators
to maintain map parts that need fixing, de-griefing or cleanup.

Others had noticed the same problems, and proposed a patch to
minetest_game. That patch is fine by itself, but it fails to add
protection bypass functionality for digging normal nodes and placing
nodes.

So, instead, we indroduce the new priv "protection_bypass" in core,
and modify 'on_place_node' and 'node_dig' to allow bypassing node
protections if the player holds this priv.

This priv was tested with protector redo by tenplus1.

A followup patch to Minetest Game will include allowing special checks
for doors, trapdoors, chests in Minetest Game.

Protection mods will likely want to mimic the changes in their relevant
code sections.

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.

Missing `valleys` in `settingtypes.txt` and `minetest.conf.example`.

If the default value of a setting was empty,
it previously generated a trailing space.

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.

Closes #3748

This makes the functions a bit faster since they don't
have to recreate the tables every invocation, and makes
the code more readable.

Also, document `wallmounted_to_dir`.

The function was implemented but not documented in `lua_api.txt`.

The engine implementation of `print` packs the varargs into a
table and passes the table directly to `table.concat`. If you
pass any value not supported by `table.concat` (particularly
`nil`), the server crashes. This is unexpected behavior, as
`print` is supposed to be able to work with anything.

This patch changes the implementation so it first converts
all arguments using `tostring`, which fixes the issue and
makes the custom `print` function compatible with the stock
Lua behavior.

Replace simple caves with V5 caves, adding unpredictable water and lava
settings and massive caves based on subterrain. Remove fast terrain mode
and accompanying settings. Remove superfluous temperature/humidity
settings. Remove lava/water height setting. Fix errors in humidity
handling and remove humidity_break_point setting. Move cave noises to
generateCaves. Fix minor formatting/naming issues and use
MYMAX/MYMIN/myround.

I could honestly not make much sense of the timer implementation
that was here. Instead I've implemented the type of timer algorithm
that I've used before, and tested it instead.

The concept is extremely simple: all timers are put in an ordered
list. We check every server tick if any of the timers have
elapsed, and execute the function associated with this timer.

We know that many timers by themselves cause new timers to be
added to this list, so we iterate *backwards* over the timer
list. This means that new timers being added while timers are
being executed, can never be executed in the same function pass,
as they are always appended to the table *after* the end of
the table, which we will never reach in the current pass over
all the table elements.

We switch time keeping to minetest.get_us_time(). dtime is
likely unreliable and we have our own high-res timer that we
can fix if it is indeed broken. This removes the need to do
any sort of time keeping.

The save button is now fully functional again when an error message
is shown.

After an invalid value is entered in the settings tab dialog, the GUI
label for the error message that is shown was partly overlapping the
'save' button, so that the top half of the button could not be clicked
on.

Changes:
- Accept setting an empty flags-type value in the settings tab
  if the variable specification permits it
- Don't accept substrings of flag values
  E.g. with values: 'one,two,three', 'hree', 'w', etc. used to
  be accepted. Not any more
- Don't accept flags with random pattern-matching special characters
  E.g. with values: 'one,two,three', 'on.', '(o)[n]e*' etc. used
  to be accepted. Not any more.

- Accept numbers prefixed with '+'
- Accept multiple spaces instead of just a single one where spaces are expected
- Allow flags to have an empty default value

The pageflip mode requires a stereo quadbuffer, and a modern graphic
card. Patch tested with NVidia 3D Vision.

The mini-map is not drawn, but that's what is done for topbottom and
sidebyside modes as well.

Also most of the time the user would prefer the HUD to be off. That's
for the user to decide though, and toggle it manually.

Finally, the interocular distance (aka eye separation) is twice as much
as the "3d_paralax_strength" settings. I find this a strange design
decision. I didn't want to chance this though, since it's how the other
3d modes interpret this settings.

Add new node property 'floodable', default false
Define "air" as floodable = true in C++ and lua

3D Mandelbrot/Mandelbar
3D Christmas Tree
3D Mandelbulb
3D Cosine Mandelbulb
4D Mandelbulb
Plus corresponding julia set for each
Add credits for formulas
Rename parameter 'formula' to 'fractal'
Speed optimisations