Determine if 'pid' is the latest version of a resource.

        Resolves True for Versioned PIDs which are the oldest of its siblings.
        False otherwise, also for Head PIDs.

def is_last_child(self, child_pid):
        """
        Determine if 'pid' is the latest version of a resource.

        Resolves True for Versioned PIDs which are the oldest of its siblings.
        False otherwise, also for Head PIDs.
        """
        last_child = self.last_child
        if last_child is None:
            return False
        return last_child == child_pid