CMake: Work around bug in FindQt4.cmake

Fixes: bug #694
CMake: Fix potential future cmake compat issue

Fixes CMP0054 warning with CMake 3.

See: bug #694
COPYING: Fix capitalization
arx-install-data: Fix whitespace/comment typos
audio: Add asserts for infinite vectors

We should really figure out the root cause here instead of checking them
at run-time.
audio: Fade out sources near the max distance

Otherwise some (loud) sources will abruptly start/stop as the player
moves towards/away from them. This problem could be reduced by setting a
higher max distance, but would still be technically there because the
inverse distance model never reaches zero gain. This may be realistic
but is undesirable if we want to cull distant sources.

This problem did not exist in vanilla AF - maybe our AL settings don't
exactly match the dsound falloff?
audio: Fix isReverbSupported() return on error
[style] Add missing brackets
[style] Add missing brackets