Safely change world.fps

- Added world.change_fps() proc to safely change world.fps
- Its important that SStimer be informed whenever world.tick_lag or world.fps change, so always use the proc, never set the var directly!

code/modules/admin/verbs/fps.dm

@@ -19,5 +19,5 @@
 	var/msg = "[key_name(src)] has modified world.fps to [new_fps]"
 	log_admin(msg, 0)
 	message_admins(msg, 0)
-	world.fps = new_fps
+	world.change_fps(new_fps)
 	feedback_add_details("admin_verb", "SETFPS") //If you are copy-pasting this, ensure the 2nd parameter is unique to the new proc!

code/modules/admin/verbs/mapping.dm

@@ -139,7 +139,7 @@ var/list/debug_verbs = list (
         ,/client/proc/cmd_assume_direct_control
         ,/client/proc/jump_to_dead_group
         ,/client/proc/startSinglo
-        ,/client/proc/fps
+        ,/client/proc/set_server_fps
         ,/client/proc/cmd_admin_grantfullaccess
         ,/client/proc/kaboom
         ,/client/proc/cmd_admin_areatest