code: func (s *Restore) Tombstone(stone *Tombstone) error {
  	if err := s.store.kvsGraveyard.RestoreTxn(s.tx, stone); err != nil {
  		return fmt.Errorf("failed restoring tombstone: %s", err)
  	}
  	return nil
  }
docs: // Tombstone is used when restoring from a snapshot. For general inserts, use
  // Graveyard.InsertTxn.