def abort(store_connection, txn=None):
    """
        Abort the commit, ignoring certain exceptions.

        If *txn* is not None, phase 1 is also aborted.

        :param store_connection: An :class:`IManagedStoreConnection`

        :return: A true value if the connection was rolled back
                 without ignoring any exceptions; if an exception was
                 ignored, returns a false value (and the connection
                 and cursor are closed before this method returns).
        """
