Skeleton key: Change to use left-click (tool on_use)

Instead of right click, the skeleton key is now a true `tool`
in the sense that it's default left-click action is to create
a key for the locked object.

This is far better than the outcome of the patches we've done
where the only way to create a key for a locked item was to
use sneak+rightclick. Now keys are perhaps a bit more sensible,
left for making keys, right for opening stuff with keys.

Fixes #1625

mods/default/tools.lua

@@ -383,22 +383,13 @@ minetest.register_tool("default:skeleton_key", {
	description = "Skeleton Key",
	inventory_image = "default_key_skeleton.png",
	groups = {key = 1},
	on_place = function(itemstack, placer, pointed_thing)
		local under = pointed_thing.under
		local node = minetest.get_node(under)
		local def = minetest.registered_nodes[node.name]
		if def and def.on_rightclick and
				not (placer and placer:get_player_control().sneak) then
			return def.on_rightclick(under, node, placer, itemstack,
				pointed_thing) or itemstack
		end

	on_use = function(itemstack, user, pointed_thing)
		if pointed_thing.type ~= "node" then
			return itemstack
		end

		local pos = pointed_thing.under
		node = minetest.get_node(pos)
		local node = minetest.get_node(pos)

		if not node then
			return itemstack
@@ -413,15 +404,15 @@ minetest.register_tool("default:skeleton_key", {
				random(2^16) - 1, random(2^16) - 1,
				random(2^16) - 1, random(2^16) - 1)

			local secret, _, _ = on_skeleton_key_use(pos, placer, newsecret)
			local secret, _, _ = on_skeleton_key_use(pos, user, newsecret)

			if secret then
				-- finish and return the new key
				itemstack:take_item()
				itemstack:add_item("default:key")
				local meta = itemstack:get_meta()
				meta:set_string("secret", secret)
				meta:set_string("description", "Key to "..placer:get_player_name().."'s "
				meta:set_string("description", "Key to "..user:get_player_name().."'s "
					..minetest.registered_nodes[node.name].description)
				return itemstack
			end