Fixing issue 706 with body classes

Still a bit to do here

- [x] get the body classes working properly on tag/cat archive pages
- [x] code clean up to match current WP standards
- [x] expand docblock to be complete
- [x] clean up wpsc_is_in_category and include term $var
- [x] clean up wpsc_is_in_tax and include term $var
- [x] clean up doc blocks

Is the formatting/clean up worth it while I'm here?

Intended to fix #706