void on_fight( object attacker, object victim )

This event has an arguably lame name, but on_attack() and on_hit() are
already quite well defined and heavily used.

The event is fired by the kill verb to notify all AI's present that a fight
is about to start. It should probably also be fired off by violent actions
in order to guarantee that everyone knows about it, but right now, this does
not happen.

FOR SCRIPTS: on_fight

Called whenever a fight starts. Actor is the person starting the fight, 
and Target is the victim.

