Tweaked Mese so that the new Mese Blocks appear where default:mese was before.

E.g. in stone where it had already been spawned in maps prior to this change,
in structures made with the old block, etc.

Mese ore (of a sort), as default:stone_with_mese, is generated now instead of
default:mese (which is not generated at all now).

The new default:mese_block is substituted in place of default:mese by way of an
alias.

Crystals still come from Mese Crystals in Stone, while digging buried Mese
Blocks returns exactly those (the same as can be crafted from 9 crystals). If
necessary, they can be split up into Mese Crystals again via the existing
crafting recipe.

This alters the value of the various Mese items a little, but avoids breaking
old structures that were made of mese.

The original default:mese, if needed, can be obtained by crafting one Mese
Crystal with one cooked stone.  Yields 1.

mods/default/init.lua

@@ -518,7 +518,6 @@ minetest.register_craft({
 	}
 })
 
-
 --
 -- Crafting (tool repair)
 --
@@ -795,6 +794,14 @@ minetest.register_node("default:stone_with_iron", {
 })
 
 minetest.register_node("default:mese", {
+	description = "Mese (Old)",
+	tiles = {"default_mese.png"},
+	is_ground_content = true,
+	groups = {cracky=1},
+	sounds = default.node_sound_stone_defaults(),
+})
+
+minetest.register_node("default:stone_with_mese", {
 	description = "Mese Crystals in Stone",
 	tiles = {"default_stone.png^default_mineral_mese.png"},
 	is_ground_content = true,
@@ -803,6 +810,8 @@ minetest.register_node("default:mese", {
 	sounds = default.node_sound_stone_defaults(),
 })
 
+minetest.register_alias("default:mese", "default:mese_block")
+
 minetest.register_node("default:dirt_with_grass", {
 	description = "Dirt with Grass",
 	tiles = {"default_grass.png", "default_dirt.png", "default_dirt.png^default_grass_side.png"},