Ported knocking on windows

code/game/objects/structures/window.dm

@@ -119,7 +119,13 @@
 		if(reinf) new /obj/item/stack/rods( src.loc)
 		src.density = 0
 		del(src)
-	return
+		return
+	else
+		playsound(src.loc, 'Glassknock.ogg', 80, 1)
+		usr.visible_message("[usr.name] knocks on the [src.name].", \
+							"You knock on the [src.name].", \
+							"You hear a knocking sound.")
+		return
 
 /obj/structure/window/attack_paw()
 	if ((HULK in usr.mutations))
@@ -436,4 +442,4 @@
 
 /obj/structure/window/reinforced/tinted/frosted
 	icon_state = "fwindow"
-	name = "frosted window"
+	name = "frosted window"