Tests failing in source distribution -- MANIFEST.in fix

Hi there,
currently when creating a source distribution the test templates are not included, which causes some of the tests to fail, so I figured you may want to add the whole tests directory, which is what this does.

Also, this is the first time I'm doing this Pull Request thingy, so please let me know if I'm doing something wrong. ^^

Regards,
Matt Stuchlik