Fixed #7143 -- Modified the test client to better match (most) real browser...

Fixed #7143 -- Modified the test client to better match (most) real browser behavior when uploading files. Now, only the file name is sent, rather than the full path. Thanks for the report, cpinto.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7577 bcc190cf-cafb-0310-a4f2-bffc1f526a37