Include SSL information in the headers for Unicorn

Unicorn is unable to get detailed SSL information because it is not exposed via the headers. This patch adds this support. There are a couple of SSL variables we aren't sending to the upstream Unicorn because it would be a lot of data (like the entire client SSL certificate ;)). See [NginxHttpSslModule](http://wiki.nginx.org/NginxHttpSslModule) for that list.