Add -4 and -6 options to flashproxy-client and flashproxy-reg-http

flashproxy-reg-email supports -4 and -6 options; if you're dual-stack, and you've configured IPv4 port forwarding, flashproxy-reg-email may connect to the SMTP server over IPv6 and register your IPv6 address, leading to confusion.

flashproxy-client should understand -4 and -6 and pass them to registration helpers that understand them. flashproxy-reg-http should use the same socket trick that flashproxy-reg-email uses.