- Add more jcr methods and make mutex and use_count private.

- Create lock/unlock methods for jcr.
- Fix PostgreSQL bug doing sql_data_seeek() by explicitly reading
  records to get to seek position.
- Integrate patch from bug #561 to correct conio.c signal definitions.
- Fix Rescheduling failed Jobs. Ensure that SD message thread
  terminates correctly by doing pthread_kill(). Do not destroy
  SD cond wait variable between executions of the job. Use local
  mutex for cond variable to avoid blocking jcr chain. Fix poor
  use of jcr use count in jobq.c for restarted jobs.
- Fix obsolete usage of foreach_dlist() to use foreach_jcr() in
  lib/jcr.c -- prevents locking the jcr chaing.
- Apply patch from bug #564, which corrects listing volumes with
  multiple autochangers. Apply same fix to next volume list.
- Fix bug #562 where restore bootstrap file is not unique.
- More details in implementing David's migration syntax proposal.
- Save and restore dcr when swapping drives so that if we have
  a write dcr it is not lost.
- Use new routine lock_reservations() to lock the reservations
  system, and call it while looking for a volume in askdir.c.
  This could possibly fix bug #543.
- Stop SD command loop if job is canceled.