- fixed psi attack formula for panic + tiny refactoring
desert hills fix. and falling behaviour fixes.

treat completely filled tiles below our tile as though they are the floor.
this will address the desert hills issues, and some other falling behaviours
while i'm at it, like TU costs and reaction fire, drawing routines for
tiles that contain items and nothing else, and walking sound effects on
these blocks.

all in all, a good night's coding.
Merge branch 'master' of https://github.com/SupSuper/OpenXcom.git into some_tests
Soldiers may to see, who kill them.