TNT: Add on_blast to all nodes with an inventory

Adds a minor helper function that allows efficient retrieval of
several inventories from a node inventory. We use this helper to
quickly retrieve the items in chests, vessel shelves, book shelves
and furnaces, and return these with the nodes itself to the TNT caller.

The TNT caller then performs the entity physics, and we don't need
to do anything else.

We disable TNT doing anything with bones.

We expose a bug in the code that drops the items - metadata was lost
entirely. This patch corrects that by properly copying the metadata
and creating the drops list inclusive metadata.

init.lua

@@ -55,7 +55,9 @@ local function eject_drops(drops, pos, radius)
 					item:get_count(),
 					item:get_stack_max()))
 			rand_pos(pos, drop_pos, radius)
-			local obj = minetest.add_item(drop_pos, item:get_name() .. " " .. take)
+			local dropitem = ItemStack(item)
+			dropitem:set_count(take)
+			local obj = minetest.add_item(drop_pos, dropitem)
 			if obj then
 				obj:get_luaentity().collect = true
 				obj:setacceleration({x = 0, y = -10, z = 0})