Fixes russian revolver being abusabled. You can no longer use it on someone other than yourself. Aiming somewhere other than head/eyes/mouth doesn't instakill but still deals damage. You need to spin the chamber after each shooting attempt. Only humans can use the gun.

Making a can_trigger_gun() proc that tests if the mob can trigger the gun.
Merge pull request #6538 from phil235/RussianRevolverFix

Fixes russian revolver being abusable.