Make it consistent with the slab recipe which conserves volume
cherry-pick from github.com/minetest/minetest_game> Mapgen: Add biome fields for riverbed node and depth
cherry-pick from github.com/minetest/minetest_game> Fire: Ignite tnt, gunpowder, permanent flame above coalblock
cherry-pick from github.com/minetest/minetest_game> Doors: Pass pointed_thing to on_rightclick() callback