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

* Horizontal and vertical are used wrongly. Use height and width because
	horizontal/vertical describes different things. Thanks @kilbith for pointing out.
* Update minetest.conf.example and settings_translation_file.cpp
* Correct maximum/minimum copy paste mistake.

Simplified the regex used, added comments and changed the error message
to contain the correct mod name.

Improve default parameters
Update and improve documentation
Unhide mapgen, but is still unstable

Flag is set by default in MapgenParams
The global 'trees' flag remains but is now
undocumented and unset by default in MapgenParams
Add mgv6_spflag 'trees' set by default in
defaultsettings.cpp to affect new worlds only
This is automatically backwards
compatible for existing worlds

Add mgv6 spflag 'flat'
Global flag is kept for backwards compatibility but is now undocumented

The player name is now added in the field "dropped_by" on the created
entity.

Add the v3f type, currently is just a nice placeholder for string.
Currently undocumented, on wish of @PilzAdam, to support future changes.

This adds a chat console the server owner can use for administration
or to talk with players.
It runs in its own thread, which makes the user interface immune to
the server's lag, behaving just like a client, except timeout.
As it uses the same console code as the f10 console, things like nick
completion or a scroll buffer basically come for free.
The terminal itself is written in a general way so that adding a
client version later on is just about implementing an interface.

Fatal errors are printed after the console exists and the ncurses
terminal buffer gets cleaned up with endwin(), so that the error still
remains visible.

The server owner can chose their username their entered text will
have in chat and where players can send PMs to.
Once the username is secured with a password to prevent anybody to
take over the server, the owner can execute admin tasks over the
console.

This change includes a contribution by @kahrl who has improved ncurses
library detection.

Use type 'string' for v3fs and add comments

Increase default from 6 to 16 to help with mgv7 and mgfractal
Large-scale or alternative mapgens can result in a lowland spawn point not
being found, causing a spawn at (0, 0, 0) possibly buried underground
The max height is now settable to allow correct player spawn
in any mapgen or when using custom noise parameters