for(var/bad_code in world)

Removes a very large amount of world loops.
Adds a macro to painlessly generate a global list, and the needed code to modify the list when an object is made or deleted automatically.
Cleans up some commented out code.

code/game/objects/items.dm

@@ -1,3 +1,5 @@
+GLOBAL_LIST_BOILERPLATE(all_items, /obj/item)
+
 /obj/item
 	name = "item"
 	icon = 'icons/obj/items.dmi'
@@ -580,7 +582,7 @@ var/list/global/slot_flags_enumeration = list(
 	I.Blend(new /icon('icons/effects/blood.dmi', "itemblood"),ICON_MULTIPLY) //adds blood and the remaining white areas become transparant
 
 	//not sure if this is worth it. It attaches the blood_overlay to every item of the same type if they don't have one already made.
-	for(var/obj/item/A in world)
+	for(var/obj/item/A in all_items)
 		if(A.type == type && !A.blood_overlay)
 			A.blood_overlay = image(I)