Support for https servers

Fairly trivial change set.

I generated the test key and cert by following Node TLS docs (http://nodejs.org/api/tls.html#tls_tls_ssl), and added a simple test to ensure the correct protocol is being detected.
@joshgillies this would have limited utility because of the quick lifecycle unless you're doing a POST/PUT and it's waiting for you to write something, or don't provide a callback and don't read from the stream for a while (i.e. it stops the server straight after it gets a response). I'd rather not expose an API unless there's a concrete use-case for it, can you come up with one?