Fixed #11270 -- Modified cache template tag to prevent the creation of very...

Fixed #11270 -- Modified cache template tag to prevent the creation of very long cache keys. Thanks to 235 for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11068 bcc190cf-cafb-0310-a4f2-bffc1f526a37