don't crash when fromNode is 0 for some reason

(it was a cyberdisk)
some code clean to remove warnings
Merge pull request #371 from hmaon/ai_continues

minor AI tweaks
fixed cyberdiscs

in case anyone cared.
ari's was more elegant.
fix for base defenses non game-over scenario after losing

... maybe

well, it should take care of unconscious or mind controlled units anyway.
make more sure the base gets unmarked.
AHAHAHA

wow.

so yeah, there's the "insane retaliation" bug fixed.
fix for bad ammo calculations

make the function return a bool as to whether the ammo can be used or not,
and don't fire a missile if we can't.
some changes in dogfight behaviour

effectively cut off use of the buttons when your craft is destroyed,
or the ufo has decided you suck and it's time to bail.
revert "make more sure the base gets unmarked."

it was fine how it was.
fix for "weird targetting near doors"
use alien mission region rather than waypoint region in hyperwave screen.
fix alien equipment

blaster bombs still screwing up.
can't figurre it out
too tires
need coffee
If deleting last save from load menu, don't show it any more.
fix interrogation popups

no longer displays racial information twice.
no longer displays alien interrogation repeatedly.
fix for previous fix
first mission is sectoids.
update camera center from inventory screen.
sanity check that variable.