def rollforward(self):
        """Restore a reverted modification to the refpkg.
        """
        if self.contents['rollforward'] is None:
            raise ValueError("No operation to roll forward on refpkg")
        new_log_message = self.contents['rollforward'][0]
        new_contents = self.contents['rollforward'][1]
        new_contents['log'] = [new_log_message] + self.contents.pop('log')
        self.contents['rollforward'] = None
        new_contents['rollback'] = copy.deepcopy(self.contents)
        new_contents['rollback'].pop('rollforward')
        self.contents = new_contents
        self._sync_to_disk()
Restore a reverted modification to the refpkg.