examine signature changed to include distance

- distance is INFINITE, 0, or a positive integer based on get_dist() between
the examiner and examinee's turfs when they are on the same Z. When the
examiner is dead or a ghost, distance is always 0.
- also updates /examine( implementations to use it!
- adds w_class_to_name proc for reusing "It is a X item." examine behavior.

code/modules/multiz/turf.dm

@@ -88,7 +88,7 @@
 
 /turf/simulated/open/examine(mob/user, distance, infix, suffix)
 	. = ..()
-	if(Adjacent(user))
+	if(distance < 2)
 		var/depth = 1
 		for(var/T = GetBelow(src); isopenspace(T); T = GetBelow(T))
 			depth += 1
@@ -189,4 +189,4 @@
 		for(var/obj/O in contents)
 			if(!O.CanFallThru(L, GetBelow(src)))
 				return TRUE // Can't fall through this, like lattice or catwalk.
-	return ..()
+	return ..()