def setReplyTo(reply_to):
    """ Make this object a response to the passed object.

        o 'reply_to' is an IDiscussable, or a path (as a string) to one.

        o Raise ValueError if 'reply_to' is not an IDiscussable (or doesn't
          resolve to one as a path).

        o XXX This does not seem like the right exception.

        o Permission: None assigned
        """
