def addgroup(deltas, linkmapper, transaction, addrevisioncb=None,
    maybemissingparents=False):
    """Process a series of deltas for storage.

        ``deltas`` is an iterable of 7-tuples of
        (node, p1, p2, linknode, deltabase, delta, flags) defining revisions
        to add.

        The ``delta`` field contains ``mpatch`` data to apply to a base
        revision, identified by ``deltabase``. The base node can be
        ``nullid``, in which case the header from the delta can be ignored
        and the delta used as the fulltext.

        ``addrevisioncb`` should be called for each node as it is committed.

        ``maybemissingparents`` is a bool indicating whether the incoming
        data may reference parents/ancestor revisions that aren't present.
        This flag is set when receiving data into a "shallow" store that
        doesn't hold all history.

        Returns a list of nodes that were processed. A node will be in the list
        even if it existed in the store previously.
        """
