def fastdelta(base, changes):
    """Obtain a delta between this manifest and another given changes.

        ``base`` in the raw data representation for another manifest.

        ``changes`` is an iterable of ``(path, to_delete)``.

        Returns a 2-tuple containing ``bytearray(self.text())`` and the
        delta between ``base`` and this manifest.

        If this manifest implementation can't support ``fastdelta()``,
        raise ``mercurial.manifest.FastdeltaUnavailable``.
        """
