clean up lots of comments / method decls. etc in npc base class
adapt npc guard command AI to mount horses if npc was commanded to guard
an applicable horse  
need to add ride-horse ai to add/remove entity attributes from mounts
fix missing mutex bits in player-owned priest ai
add ride-horse ai to add/remove appriate modifiers from horse mounts for
player-owned npcs  
need to adapt AI for faction-owned horse riders to spawn their horse if
not present (if not already killed).