Merge pull request #9632 from Ghommie/Ghommie-cit281

Porting multi-z support updates.

code/game/objects/effects/decals/decal.dm

@@ -15,7 +15,7 @@
 		qdel(src)
 
 /obj/effect/decal/proc/NeverShouldHaveComeHere(turf/T)
-	return isspaceturf(T) || isclosedturf(T) || islava(T) || istype(T, /turf/open/water) || ischasm(T)
+	return isclosedturf(T) || isgroundlessturf(T)
 
 /obj/effect/decal/ex_act(severity, target)
 	qdel(src)

code/game/objects/effects/effects.dm

@@ -57,6 +57,9 @@
 /obj/effect/abstract/singularity_act()
 	return
 
+/obj/effect/abstract/has_gravity(turf/T)
+	return FALSE
+
 /obj/effect/dummy/singularity_pull()
 	return