[PATCH] Session helper: upgrade DB and fix active mode

Further to discussions, please find attached a patch for the session
helper to:

- Remove support for Berkeley DB 1.85
- Add support for the current Berkeley DB (db.h)
- Add support for a DB environment (fixes synchronisation between
multiple processes)
- Fix the active mode bug previously submitted (but not accepted)

I admit that I am rushing to submit this as I go away for the weekend,
so please let me know if it's not up to scratch! Works For Me (TM)
though.

Thanks,

Andy