Tweaked templates/builtins.txt to make it clearer that cycle and firstof...

Tweaked templates/builtins.txt to make it clearer that cycle and firstof filters don't auto-escape. Refs #10912

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17177 bcc190cf-cafb-0310-a4f2-bffc1f526a37