Fixes #3291

Thanks to @arpruss for reporting the bug, and suggesting the fix.

Also, remove trailing whitespaces.

Previously, xgettext failed to resolve the dynamic call.
Thanks to @JakubVanek for pointing this out.

-> Get rid of Logger::logToSystem and use normal downstream output system for android instead

-> Give the downstream output system more information: enrich the log function of ILogOutput
	with information and add ICombinedLogOutput for easier use.

-> Make Logger::getLevelLabel() static and public so that it can be used by downstream log output.

-> Add g_ and m_ prefixes where required

* Add key settings to setting table and ignore them later
  This way they are added to the auto-generated minetest.conf.example
* Add flags type
* Add input validation for int, float and flags
* Break in-game graphic settings into multiple sections
* Parse settingtpes.txt in mods and games
* Improve description for a lot of settings
* Fix typos and wording in settingtypes.txt
* Convert language setting to an enum

Thanks to SmallJoker for pointing this out.

fixes https://github.com/minetest/minetest_game/issues/537

Index more columns in the action table of the rollback DB to improve the performance of /rollback_check

Flushes the buffer of rollback actions that wait to get saved in two more situations:

1. Flushes in the destructor of the rollback. This makes the server not
forget the last < 500 rollback entries when it shuts down.

2. Flushes the rollback when /rollback_check is invoked. This is neccessary
as otherwise it leads to confusion if users want to test the rollback functionality
by placing a node and then executing the check on it, or if the actions were
very recent out of other reasons.

- Fix thread name reset on start()
- Fully reset thread state on kill()
- Add unittests to check for correct object states under various circumstances

Add findLiquidSurface() function to mapgen.cpp
Update lua_api.txt

The callback can now be invoked with either the player object or name as
the first parameter, and with either a table or a list of strings, like
this:

    minetest.check_player_privs(player_name, { shout = true, fly = true })
    minetest.check_player_privs(player_name, "shout", "fly")
    minetest.check_player_privs(player, { shout = true, fly = true })
    minetest.check_player_privs(player, "shout", "fly")

Currently translated at 72.6% (202 of 278 strings)

Currently translated at 100.0% (278 of 278 strings)

Currently translated at 100.0% (278 of 278 strings)

Fixes #3262.

Default is true for backwards compatibility
Update lua_api.txt

Everywhere where wstrgettext was used, its output was converted back
to utf8. As wstrgettext internally converts the return value
from utf8 to wstring, it has been a waste. Remove the function, and
use strgettext instead.

According to its man page, the function gettext(3)
"may return a nonempty string" when msgid is "".

This commit fixes a bug where the comment ""
for some settings caused gettext to return a
"nonempty string", in this case header info of the
po file.

- setOpenedTrees(): this internal function was calling setSelected()
  to update m_selected. Since setSelected() calls autoScroll(),
  this caused the scrollbar to scroll back to the selected row
  in some cases when that shouldn't be done.

  For example, clicking the "+" to open a tree caused autoscroll.

  Fix this by making setOpenedTrees() modify m_selected directly.

- setDynamicData(): set scrollbar position after calling
  setSelected(), not before. This avoids setSelected()'s autoscroll
  messing up the scrollbar position again.

- setSelected(): If an invisible row is selected, open all parents
  of the selected row in order to make the selected row visible.

  This fixes the issue where all the trees are closed again whenever
  you return from the setting edit dialog to the settings tab.

Passing line numbers in the comments is bad.

References:

* Commit 94961b33
* Previous commit

Settings are automatically parsed from builtin/settingtypes.txt
The edit dialog automatically adjust based on the type of setting

- Fix some incompatibilities with obscure platforms (AIX and WinCE)
- Clean up Thread class interface
- Add m_ prefix to private member variables
- Simplify platform-dependent logic, reducing preprocessor
  conditional clauses and improving readibility
- Add Thread class documentation

- Add "thr_" prefix to thread utility functions
- Compare threadid_ts in a portable manner, where possible

The invsize formspec element is outdated. Even though,
it is still supported, only a deprecation warning is shown,
introduced by commit [1]. The lua context passed to the
log_deprecated method added by commit [1] is NULL for the
invsize deprecation warning, as its run on the client and not
the server.

Commit [1] has removed checks for NULL inside the log_deprecated
method, resulting in a crash when a formspec with an invsize
element is parsed. This commit puts the check back.

Fixes #3260.

Referenced commits:

[1]: b5acec0a "Add proper lua api deprecated handling"

[2]: 7b8d3729 "Use warningstream for deprecated field messages and refactor log_deprecated"

Commit

d2ca6625 "Enforce hiding nametag"

didn't fix the issue for "client" instances, where the nametag update
was received before the object was added to the scene. This resulted
in the grey shadow on the nametag that commit tried to fix.

Thanks to @neoascetic for pointing out that there still is a shadow.

Used PNGOUT, OptiPNG and DeflOpt.
Removes ~350 KB without any loss in quality.

All log operations are now added to the syslog implicitly.
Also, pass along mutable string to argument vector for main().

These names are reserved for the compiler/library implementations.

Remove DTIME macro and its uses, too

- Add warning log level
- Change debug_log_level setting to enumeration string
- Map Irrlicht log events to MT log events
- Encapsulate log_* functions and global variables into a class, Logger
- Unify dstream with standard logging mechanism
- Unify core.debug() with standard core.log() script API