refactor 'dir = ' into 'set_dir()'

This should have little/no gameplay effect right now, just paving the
 way for directional lights.
Replaced handle_rotation() on buckly things with this.

Signed-off-by: Mloc-Argent <colmohici@gmail.com>

code/game/objects/items/weapons/grenades/grenade.dm

@@ -35,7 +35,7 @@
 		spawn(det_time)
 			prime()
 			return
-		user.dir = get_dir(user, target)
+		user.set_dir(get_dir(user, target))
 		user.drop_item()
 		var/t = (isturf(target) ? target : target.loc)
 		walk_towards(src, t, 3)