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

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();