Fixed #8381 -- Fixed a problem with appending slashes in the common middleware

when SCRIPT_NAME contains something other than '/'. Patch from jcassee.

Also fixed the middleware tests to work with this patch.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8456 bcc190cf-cafb-0310-a4f2-bffc1f526a37