ItemStack is a struct, not a class
CollisionInfo is a struct, not a class
InventoryAction is abstract and it needs a virtual destructor

Inventory menu (with dragging) improved. Crafting is now handled via a IACTION_CRAFT inventory action.

The huge item definition and item namespace unification patch (itemdef), see http://c55.me/minetest/wiki/doku.php?id=changes:itemdef