Updated cart action for when a product is added to the cart.
Also incorporated functionality for updating the cart when from
within the shopping cart.  Displays error message(s) when adding
items to the cart.

Testing requested!

Modified the resync properties of the admin to basically not set
the remaining balance to zero if the Sync Quantities option is
selected on a non-SBA tracked items.
Catch up commit.
Merge branch 'mc12345678' of https://github.com/potteryhouse/stock_by_attribute_1.5.4.git into mc12345678

Conflicts:
	includes/extra_cart_actions/stock_by_attributes.php