small fix in walk sound stuff

stops everyone making the flying sound even if they don't fly
because the TFTD flying sound REALLY doesn't fit this.
fix small error on civilian units
Merge branch 'master' of https://github.com/SupSuper/OpenXcom into oXc_kL

Conflicts:
	src/Battlescape/UnitSprite.cpp
	src/Battlescape/UnitWalkBState.cpp