This patch adds code for connecting through SOCKS5 proxies. It was
primarily written for use with TOR, so there are some open issues:
* it only allows to make proxy requests with full hostnames; ipv4/ipv6 is
not supported
* GSSAPI authentication (which is mentioned as mandatory in RFC 1928) is
not implemented
* plaintext authentication is untested
To use it
* set 'proxy_type' to 'socks5'
