- set hostname in CLI prompt

- add assertions to help identify odd LASTSEEN breakage
- make cluster_hb_interval work; include interval/timeout in heartbeats
  so that a change on the master is propagated immediately to the slaves
- use fast heartbeats when there are slaves not up to date
- ensure basetime of shut down master is set to zero (prevent delayed election)
- fix radius session leak on IPCP timeout
- fix some off-by-one errors in tunnel/session loops