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)

Currently translated at 100% (0 of 0 strings)

Created new translation.

Currently translated at 21.4% (169 of 787 strings)

Currently translated at 44.0% (347 of 787 strings)

Currently translated at 25.4% (200 of 787 strings)

Currently translated at 40.2% (317 of 787 strings)

Currently translated at 100.0% (787 of 787 strings)

Currently translated at 96.8% (762 of 787 strings)