No kill stealing

Note that this does NOT cover loot stealing.

The problem:
* Player starts a fight with an enemy and just as they're about to kill it, someone else intrudes on the fight and kills the enemy instead, receiving the experience and any loot one would get from it instead of the person who handled most of the fight.

Solutions:
* Enemy lock; even if you can "kill steal" by delivering the killing blow, the kill and loot is awarded to the person or party who started the fight. Essentially wasting the intruder's effort.
* Shared victory, the person who intrudes is treated as if they were a party member.
* Dungeon instances; anyone who could kill steal are already member of your team