Multi-z fixes.

code/modules/multiz/structures.dm

@@ -61,8 +61,7 @@
 	opacity = 0
 	anchored = 1
 
-	New()
-		. = ..()
+	initialize()
 		for(var/turf/turf in locs)
 			var/turf/simulated/open/above = GetAbove(turf)
 			if(!above)

code/modules/multiz/turf.dm

@@ -13,8 +13,9 @@
 
 /turf/simulated/open/New()
 	. = ..()
-	ASSERT(HasBelow(z))
-	below = GetBelow(src)
+	spawn(1)
+		below = GetBelow(src)
+		ASSERT(HasBelow(z))
 
 /turf/simulated/open/Entered(var/atom/movable/mover)
 	// only fall down in defined areas (read: areas with artificial gravitiy)