openvt,getty,vfork_daemon_rexec,mount: tighten up fd cleanup code

(will close all fd's > 2 on daemonization now)
getty: fix "getty -" support, and also do not try to chown/chmod "-"
telnetd: fix "lost ctty" bug
Yet another attempt on saner function names:
bb_sanitize_server_stdio(0/1) -> bb_sanitize_stdio() + bb_daemonize();

debianutils/start_stop_daemon.c

@@ -291,8 +291,8 @@ int start_stop_daemon_main(int argc, char **argv)
 	}
 	*--argv = startas;
 	if (opt & OPT_BACKGROUND) {
-		xdaemon(0, 0);
 		setsid();
+		bb_daemonize();
 	}
 	if (opt & OPT_MAKEPID) {
 		/* user wants _us_ to make the pidfile */