Fix active ghoststones being droppable with sand

Fixes #289

mesecons_random/init.lua

@@ -53,6 +53,7 @@ minetest.register_node("mesecons_random:ghoststone_active", {
 	diggable = false,
 	sunlight_propagates = true,
 	paramtype = "light",
+	drop = "mesecons_random:ghoststone",
 	mesecons = {conductor = {
 		state = mesecon.state.on,
 		rules = {