use byte 61 in MCD

it's the "xcom facility item" flag
add a 3-dimensional array for base modules

a 6x6 grid, 2 deep, containing info on how many destructible objects
were present at map beginning, and how many were/are left now.
won't break saved games.

AI will be attracted to non-defunct modules, and try to destroy them.
anyone destroying a critical component will lower the "current score" for
that module, when this hits 0, AI will pass it over.
destroy facilities after base missions

so if the aliens (or you) destroy a facility during a base defense mission,
that may have certain consequences, like cancelling a manufacturing project
or destroying a craft.
destroy disconnected facilities as well.

if a base module is destroyed in combat, it may break the connectivity
of other modules on the base. account for that shit.
remove unused "destructible" flag from ruleset
yay gravity fixes.
pixel fix for pathfinding thing
fix some broken walls in alien bases and abductors
fix sanity check
ammendments to facility destruct sequence
tidyin
fix typo

thanks to cfailde for pointing this out.
some explosion tweakage

don't start any explosions at a frame above 0, instead, range the starting
frame between 0 and -4 (meaning a 4 frame delay) and layer the explosions
accordingly. distribution should be more or less equal between these frame
delays.
Fix broken string
Merge pull request #773 from cfailde/string

Fix broken string
account for carried comrades at debriefing.

turns out i forgot to include this in debriefing, having only applied it to
units actually reviving from unconsciousness.
sanity check for good luck.
no reaction fire with unresearched weapons.
battleAutoEnd... we meet again.
save motion points.