Optimized {% cycle %} template tag so that it creates the Variable objects in...

Optimized {% cycle %} template tag so that it creates the Variable objects in CycleNode.__init__() rather than each time render() is called

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7756 bcc190cf-cafb-0310-a4f2-bffc1f526a37