Too remove potential excessive garbage collection per tick. We will be reusing lists for overlays instead of deleting and creating them.

the .Cut() proc on a list will empty a list by default. This also will set the len to 0.

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@5465 316c924e-a436-60f5-8080-3fe189b3f50e

code/modules/reagents/Chemistry-Reagents.dm

@@ -844,7 +844,7 @@ datum
 				if(volume >= 5)
 					if(istype(T, /turf/simulated/wall))
 						T:thermite = 1
-						T.overlays = null
+						T.overlays.Cut()
 						T.overlays = image('icons/effects/effects.dmi',icon_state = "thermite")
 				return
 
@@ -1034,7 +1034,7 @@ datum
 						O.clean_blood()
 			reaction_turf(var/turf/T, var/volume)
 				if(volume >= 1)
-					T.overlays = null
+					T.overlays.Cut()
 					T.clean_blood()
 					for(var/obj/effect/decal/cleanable/C in src)
 						del(C)

code/modules/reagents/reagent_containers/glass.dm

@@ -112,7 +112,7 @@
 		update_icon()
 
 	update_icon()
-		overlays = null
+		overlays.Cut()
 
 		if(reagents.total_volume)
 			var/image/filling = image('icons/obj/reagentfillings.dmi', src, "[icon_state]10")

code/modules/reagents/reagent_containers/syringes.dm

@@ -168,7 +168,7 @@
 
 	update_icon()
 		var/rounded_vol = round(reagents.total_volume,5)
-		overlays = null
+		overlays.Cut()
 		if(ismob(loc))
 			var/injoverlay
 			switch(mode)