code: public Iterable<Location> undo(Location end) throws ClosedJournalException, CompactedDataFileException, IOException {
          return new Undo(redo(end));
      }
docs: Return an iterable to replay the journal in reverse, starting with the
  newest location and ending with the specified end location. The iterable
  does not include future writes - writes that happen after its creation.
  
  @param end
  @return
  @throws IOException
  @throws CompactedDataFileException
  @throws ClosedJournalException