Clean up check for item being equipped

Moved some common code to item.dm. Someone should probably take a look
at get_equipped_items() in inventory.dm sometime in the future.

code/game/objects/items.dm

@@ -271,6 +271,18 @@
 /obj/item/proc/equipped(var/mob/user, var/slot)
 	return
 
+//returns 1 if the item is equipped by a mob, 0 otherwise.
+//This might need some error trapping, not sure if get_equipped_items() is safe for non-human mobs.
+/obj/item/proc/is_equipped()
+	if(!ismob(loc)) 
+		return 0
+	
+	var/mob/M = loc
+	if(src in M.get_equipped_items())
+		return 1
+	else
+		return 0
+
 //the mob M is attempting to equip this item into the slot passed through as 'slot'. Return 1 if it can do this and 0 if it can't.
 //If you are making custom procs but would like to retain partial or complete functionality of this one, include a 'return ..()' to where you want this to happen.
 //Set disable_warning to 1 if you wish it to not give you outputs.

code/game/objects/items/weapons/storage/belt.dm

@@ -10,12 +10,7 @@
 
 
 /obj/item/weapon/storage/belt/proc/can_use()
-	if(!ismob(loc)) return 0
-	var/mob/M = loc
-	if(src in M.get_equipped_items())
-		return 1
-	else
-		return 0
+	return is_equipped()
 
 
 /obj/item/weapon/storage/belt/MouseDrop(obj/over_object as obj, src_location, over_location)