- Tweak dvd-writepart script to prevent door from opening/closing

  so much.
- Remove GROUP BY in several PostgreSQL commands to prevent error.
  Resolves bug report.
- Ensure that < as first character of filename list is not treated
  as a directory for restore.
- Add debug to heartbeat in FD as it seems to go into an
  infinite loop from time to time during SD failure in DVD writing.
- Add more debug code to dvd writing.
- Attempt not to destroy existing fs on DVD.