Revolution game mode fixes:

Station-heads who are monkied now count as 'dead' for round completion.
- This previously applied to revheads but not station heads.

Changed get_all/living_heads to pull from the mob list instead of the player list.
- It was causing players to get skipped by the check-antag verb admins have if they were disconnected.

Runtime fix by Erro for:
runtime error: Cannot execute null.show inv().
proc name: done (/obj/effect/equip_e/human/done)
  source file: inventory.dm,562
  usr: Nodrak Davis (/mob/living/carbon/human)
  src: the human (/obj/effect/equip_e/human)
  call stack:
the human (/obj/effect/equip_e/human): done()
the human (/obj/effect/equip_e/human): process()

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@4509 316c924e-a436-60f5-8080-3fe189b3f50e

code/modules/mob/living/carbon/human/inventory.dm

@@ -557,7 +557,7 @@ It can still be worn/put on as normal.
 					source.update_icons()
 					target.update_icons()
 
-	if(source)
+	if(source && target)
 		if(source.machine == target)
 			target.show_inv(source)
 	del(src)