(server_init): Initialize liboop.  Adjusted to the new isc API:s.
(sighandler_hup): Now an liboop signal callback, not a real signal
	handler.
(sighandler_quit): Ditto.
(sighandler_usr2): Ditto.
(sighandler_usr1): Ditto.  Do the real work here.
(sighandler_winch): Ditto.  Do the real work here.
(setup_sighandlers): Removed.
(restart_syscalls_on_intr): Removed.
(intr_syscalls_on_intr): Removed.
(main): Clean up liboop structures on shutdown.