[1.2.X] Improved example to account for environments where cStringIO is not...

[1.2.X] Improved example to account for environments where cStringIO is not available. Thanks to rubic for the report and niall for the patch.

Backport of [14076] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14077 bcc190cf-cafb-0310-a4f2-bffc1f526a37