fixes to #ifndef guards, a new makefile with pch

Using precompiled headers with gcc saves about 25% on the total compie time for OXC. That could help when frequently recompiling the project for debugging.
some flags and clean
missing ref
Debian packaging files for v0.5.0 release
libyaml-cpp version declaration
Menu entries installed incorrectly
fix for panicked MCed units
fix for door fix
keep track of units spotted this turn

so we don't stop if we re-spot a unit we've already seen this turn.
un-kneeling as the first step of a walk action (visual fix)
yet more changes in pathfinding

sigh. so much redundancy.
let the isBlocked function take care of pathing through other units.

let the walk state worry about whether or not we can walk to the tile
in question, and charge cost any TUs if you can't.
notify us of chryssalid kills.
make sure dead units can't see a damn thing.
don't keep MCed aliens visible when we shouldn't.
add extra clips to xcom

do a second pass on xcom units and assign them an extra clip, if available.
save kill count for battleUnits
midi makes me sad in my face.
to hell with it.

i'm so freaking sick of enemies not moving because of blocked paths, i've
made an executive decision to allow enemy units to pathfind through eachother
regardless and just consider tiles with units in them as "more expensive"
(the walk state will still disallow this type of movement.
fix for previous screw-up
de-transpose digits