Your documentation is full of mistakes. Latest one I found was at http://docs.getshopped.org/documentation/wpsc_end_category_query/
In this case, you state wpsc_end_category_query() is in category.functions.php. It is not. After near 2 hours, I found it in /wp-content/plugins/wp-e-commerce/wpsc-components/theme-engine-v1/helpers/product.php
You have made it abundantly clear on your website that you don't care to be contacted unless we pay you. So, I have no choice but to publicly ask you to sift through the outdated and wrong info on your documentation.