Fixed #6497 -- Improved fixture error reporting by displaying the entire...

Fixed #6497 -- Improved fixture error reporting by displaying the entire traceback. Also, SystemExit and KeyboardInterrupt now exit the script properly. Thanks for the patch, Bastian Kleineidam

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7653 bcc190cf-cafb-0310-a4f2-bffc1f526a37