new ansivar 'melee_ally'

  There's a new ansivar in town, called 'melee_ally', which will start with 
  the same value as 'melee'.  It is used in place of 'melee' when the thing 
  being attacked is a player or owned mob (like a summon, guild follower, or 
  merc).  If you want a nice colorful warning when non-tank is getting hit, 
  this could be a useful var to set.