Fixed #14468 -- Extended the list of content types that the test client could...

Fixed #14468 -- Extended the list of content types that the test client could guess when handling zip files. Thanks, Russ and emulbreh.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15236 bcc190cf-cafb-0310-a4f2-bffc1f526a37