uc_ajax_cart should use attachBehaviors to notify other modules of cart reloads

uc_ajax_cart is uses Drupal behaviors to respond to other module's changes, but it does not notify other modules when it reloads the cart dynamically. This becomes apparent when using uc_discounts_alt and changing a product quantity or removing a product for example. The discount message appears initially on the cart page, but then disappears after a AJAX cart update.