When all items are removed from the cart make sure the ec_checkout_id is unset to allow deletion of the session.

Add tests to make sure that when you have an anonymous only product it will not allow registered only products to be added to the cart, and vice versa.

Fix up paradox in that you can have both products with anonymous and registered in the cart at the same time.

Add new purchase policy to allow products that can only be purchased by registered users, but still allow anonymous users to add them to their cart.

Charge order of checks for determining if a product checkout is a form or a link to be more efficient.

#1125266 by wmckinley: Fixed '&' interpreted as & on token [txn:txn-items]  in rules for order confirmation.

- added load functions so that tangible items are now shown "as shippable". This allows the display of shipping dimensions fields to only appear on products that are shippable.