using linear + binary search.

On non-windows platforms this just used a semaphore,
which meant that multiple calls to signal() would
result in wait() returning multiple times.

This is set to the XDG cache path where possible.
It's set to the app's cache path on Android.

Fix the type of the threshold value for mapgen.
The commit

a78dd7f2 "Fix spelling of noise_threshold"

has changed it to be read as int, but it can have non-integral values too.

Thanks to @kwolekr for pointing this out.

If rendered as markdown, lists need a blank line before them
so that they are recognized as such.

To terminate unwanted shadows from floatlands or realms above
Also add to LuaVoxelManip calc_lighting for use in mapgen mods
Remove the 2 argument calcLighting, mapgens now use the 5
argument form to specify the volumes for propagateSunlight and
spreadLight
In mgsinglenode replace calcLighting with setLighting and
clean-up use of tabs and spaces

On openSUSE luajit is not detected correctly.
This is because openSUSE is using a lua version suffix, like other Linux distributions do it also.
So the include directory is:
include/luajit-5_1-2.0

Now we do sudo apt-get update to download package sources.
This fixes travis build with the new GCE based infrastructure.

Closes #3427.
Closes #3426.

openSUSE sets that option to ON.

Fixes #3420.

Mgv7/flat/fractal: Reduce tunnel noise spreads to 96

A segfault exposed a missing 'vm->m_area.contains()'
check in makeCorridor that allowed the calculation
of vm index for a node outside the vm area. The huge
and invalid index number caused getContent to fail

For future river mapgens
Dungeons will not generate in river water, to
avoid dungeons filling and blocking river channels

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

Fixes bug for which commit

6c37e89f "Fix old client showing duplicated health bar on new server"
by @sapier

laid the groundwork, where the server has
updated its copy of the hud flags without
respecting the mask.

Fixes #3395.

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

Recent irrlicht revisions break the build, hardcode the revision to a working one
until upstream publishes a working version. See issue #3366 for
a discussion about this.

Also update dependencies to current versions.

Currently translated at 42.0% (331 of 787 strings)

Currently translated at 45.8% (361 of 787 strings)

Currently translated at 32.4% (255 of 787 strings)

Currently translated at 45.7% (360 of 787 strings)

Currently translated at 45.6% (359 of 787 strings)

Currently translated at 100.0% (787 of 787 strings)

Currently translated at 26.3% (207 of 787 strings)

-

Currently translated at 11.8% (93 of 787 strings)

Currently translated at 31.6% (249 of 787 strings)

Currently translated at 31.6% (249 of 787 strings)

Currently translated at 41.4% (326 of 787 strings)

Currently translated at 100.0% (787 of 787 strings)

Currently translated at 9.2% (73 of 787 strings)

Currently translated at 100.0% (787 of 787 strings)