Remove wpsc_core_store_use_shipping() in favor of wpsc_is_shipping_enabled()
We had inverted logic in wpsc_is_shipping_enabled().  This is why best practices dictate positive flags.
Regions update correctly on shipping same as billing change
When shipping same as billing changes the country drop downs need to be updated first, then the region drop downs need to be filled with the current correct regions, then the current region needs to be set.

This change enforces this dependency order so that display is correct

Resolves issue #1280
Merge branch 'pr-1280-shipping-same-as-billing-change-region-update' into branch-3.8.14.1-dev