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();

util-linux/mount.c

@@ -737,7 +737,7 @@ static int daemonize(void)
 	dup2(fd, 0);
 	dup2(fd, 1);
 	dup2(fd, 2);
-	if (fd > 2) close(fd);
+	while (fd > 2) close(fd--);
 	setsid();
 	openlog(applet_name, LOG_PID, LOG_DAEMON);
 	logmode = LOGMODE_SYSLOG;