Serious efficiency fixes to last few commits

ship.findNearestStation()
Allow fleeing to witchspace in certain situations
Prefix internal cache names with oolite_
Cache system.stations values rather than searching all entities every time
Fix bug in friendly/hostile/trading station selection
Slightly optimise conditionLosingCombat, and fix bug in witchspace flee
conditionInCombat is called on just about every AI reconsideration; optimise it
Fix bug in acquireCombatTarget

-DDEBUG_LASER_TYPES compile-time option to allow easier visual inspection of the "autoWeapons" changes