Revert unnecessary AJAX URL abstractions.

2d6896eac2fad7ca4f5eebc34864df7ae0eb980e introduced wpsc_admin_ajax_url() and wpsc_ajax_url(), which are an unnecessary abstraction of ajaxurl.
First pass (read: might break stuff) at renaming some of our recently revamped JS object variables.
Merge branch 'master' of github.com:wp-e-commerce/WP-e-Commerce