Minimum cart item quantity for checkout

As it exists currently, a minimum order amount can be specified to allow checkout, but there is no clear method for setting up a requirement for a minimum number of items to allow checkout.

This patch adds an additional field to the cart settings form at admin/store/settings/cart/edit/basic that allows a site admin to specify a minimum quantity of items to require in the cart before allowing a user to proceed to checkout. This is based on the total number of cart items, whether split between multiple products, or multiples of a single product. If the value is 0, checkout will always be allowed, so this patch can be rolled into any installation without worry about having to establish a minimum item count requirement for checkout.

Installation & Usage:

Place patch file into modules/ubercart and apply. Affected files are uc_cart.pages.inc and uc_cart.admin.inc
Navigate to admin/store/settings/cart/edit/basic and set a minimum order items value. Last item in the General Cart Settings form pane