Database Upgrade Routine to rename old _wpsc_* product metadata array keys so they no longer include the '_wpsc_' prefix

Fixes #492
Changelog for database upgrade routine
Remove debugging statement
Use strict comparison and fix whitespace issues

As per feedback from @JustinSainton.
Should now match http://make.wordpress.org/core/handbook/coding-standards/php/.
Merge pull request #493 from om4james/productmeta

Database Upgrade Routine to rename old _wpsc_* product metadata array