Bug#105476: proc and auth not robust

[Roland McGrath]

You know, it might not hurt to add `ports_interrupt_rpcs (p);' at the end
of process_has_exited (mgt.c).  That would e.g. interrupt
auth_server_authenticate in S_proc_reauthenticate (now that the lock is not
held across the call), which in theory will be getting aborted by auth when
the rendezvous port dies (but what if the client used a bogus long-lived
rendezbous port that didn't die when he was killed?).

Off hand I don't know that there are any other blocks in proc that would be
interrupted by this.