Fixed #13567 -- Added a 'silent' argument to the cycle tag, so that you can...

Fixed #13567 -- Added a 'silent' argument to the cycle tag, so that you can declare a cycle without producing a value in the template. Thanks to anentropic for the suggestion and initial patch, and Łukasz Rekucki for the final patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14439 bcc190cf-cafb-0310-a4f2-bffc1f526a37