Players are no longer implicitly zombies if they're not humans. Players are no longer implicitly humans if they're not zombies. This is preparation for a third, optional spectator team. A few small optimizations and fixes.
Consider possibility of nil or NULL being a value in the tables returned from util.FindInSphere, util.FindInBox, and ents.GetAll.
Added fists. Fixed insane knockback on melee. Ragdolls on zombies now knocked back by melee/stone deaths.
