Returns a list of dataruns, in order.

def _get_dataruns(self):
        '''Returns a list of dataruns, in order.
        '''
        if self._data_runs is None:
            raise DataStreamError("Resident datastream don't have dataruns")

        if not self._data_runs_sorted:
            self._data_runs.sort(key=_itemgetter(0))
            self._data_runs_sorted = True

        return [data[1] for data in self._data_runs]