Fixed #6997 -- Corrected `num_pages` calculation when one item is in the...

Fixed #6997 -- Corrected `num_pages` calculation when one item is in the object list and `allow_empty_first_page=False`, thanks to framos for the report.  Also, made Page's `start_index()` return 0 if there are no items in the object list (previously it was returning 1, but now it is consistent with `end_index()`).  As an added bonus, I threw in quite a few pagination tests.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8129 bcc190cf-cafb-0310-a4f2-bffc1f526a37