Fixes and tidying up of Also Bought code.

This fixes:

1. some SQL errors that happen when checking out.
2. some product name references
3. uses the more recent 'no image' image.

It also calls the wpsc_populate_also_bought_list() function via the 'wpsc_submit_checkout' action so that it can easily be easily removed by a plugin in the transition period when this functionality is deprecated.