IPv6 support

Nginx will listen on both ipv4 and ipv6. It should be compiled with `--with-ipv6` option.

I don't think this one is a good idea, I don't consider it a good practice anyway.

A client without [SNI](http://en.wikipedia.org/wiki/Server_Name_Indication) will not send the hostname when establishing a connection. So they'd always end up here, even if they requested `https://valid.com`.