Small Docs edit in variations.class.php

Maybe the first of a few changes here.
Initial top-of-file docs for productfeed.php
Small alignment fix in productfeed.php
Initial Docs for checkout-form-data.class.php
Initial Class Doc for checkout-form.class.php

and whitespace fixes
First docs within wpsc-admin/media.php

The first docs, ever. I hope I'm doing this right :)
'not_found' label for Product Tags
customer-ajax.php @package and @since 

For top of file docs
fixing media.php docs
Merge pull request #1714 from NikV/Inline-docs

Inline Docs (Round 4)