Stop mesecon pistons pushing frame/pedestal

This pull checks for mesecons_mvps mod and adds the item frame and
pedestal items to the list of non-movable items so that players cannot
exploit the double-item glitch.

mesecons_mvps added to depends.txt file for this to work.

itemframes/depends.txt

@@ -1 +1,2 @@
 default
+mesecons_mvps?

itemframes/init.lua

@@ -253,3 +253,9 @@ minetest.register_craft({
 		{'default:stone', 'default:stone', 'default:stone'},
 	}
 })
+
+-- stop mesecon pistons from pushing itemframes and pedestals
+if minetest.get_modpath("mesecons_mvps") then
+	mesecon.register_mvps_stopper("itemframes:frame")
+	mesecon.register_mvps_stopper("itemframes:pedestal")
+end