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/game/objects/structures/barsign.dm

@@ -15,7 +15,7 @@
 	if(initial)
 		. -= "Off"
 
-/obj/structure/sign/double/barsign/examine(mob/user)
+/obj/structure/sign/double/barsign/examine(mob/user, distance, infix, suffix)
 	. = ..()
 	switch(icon_state)
 		if("Off")