isopenturf() macro, update_above improvements (#2931)

changes:

Added a isopenturf() macro, equivalent to istype(thing, /turf/simulated/open).
Converted most/all instances of istype(/turf/simulated/open) to isopenturf().
Made update_above()' aware of queue status & inlined a proc-call.

code/controllers/subsystems/falling.dm

@@ -78,10 +78,10 @@
 		// Invokes fall_through() after the atom is moved to
 		// its new destination this cycle. Immediately invokes fall_impact and
 		// fall_collateral if the next turf is not open space.
-		if (istype(victim.loc, /turf/simulated/open))
+		if (isopenturf(victim.loc))
 			victim.forceMove(below)
 
-			if (istype(victim.loc, /turf/simulated/open))
+			if (isopenturf(victim.loc))
 				victim.fall_through()
 			else
 				// This is a lookahead. It removes any lag from being moved onto

code/controllers/subsystems/initialization/minimap.dm

@@ -2,7 +2,7 @@
 // Seems to be much simpler/saner than /vg/'s implementation.
 
 // Turfs that will be colored as HOLOMAP_ROCK
-#define IS_ROCK(tile) (istype(tile, /turf/simulated/mineral) || istype(tile, /turf/simulated/floor/asteroid) || istype(tile, /turf/simulated/open))
+#define IS_ROCK(tile) (istype(tile, /turf/simulated/mineral) || istype(tile, /turf/simulated/floor/asteroid) || isopenturf(tile))
 
 // Turfs that will be colored as HOLOMAP_OBSTACLE
 #define IS_OBSTACLE(tile) ((!istype(tile, /turf/space) && istype(tile.loc, /area/mine/unexplored)) \

code/controllers/subsystems/openturf.dm

@@ -195,6 +195,6 @@
 
 /datum/controller/subsystem/openturf/proc/calculate_depth(turf/simulated/open/T)
 	. = 0
-	while (T && istype(T.below, /turf/simulated/open))
+	while (T && isopenturf(T.below))
 		T = T.below
 		.++