- Show session open time in "show session"/"show user" detailed output.

- Have slaves with BGP configured drop BGP on receipt of a shutdown
  signal, but hang about for an additional 5s to process any remaining
  traffic.
- Replace MAX_ACTIONS with a "cleanup_limit" config option, drop the
  default for "cleanup_interval" to 2s (so as to process tunnel/RADIUS
  retries more promptly).