Port to Jetty 9.

I have an interest in running SPDY in ring, and so I took a crack at https://github.com/ring-clojure/ring/issues/80. My work is incomplete. I'm submitting this now for comments. I'd like to know if I'm on the right track. This doesn't add SPDY. This just ports to Jetty 9. Supposedly Jetty 9 now requires a 1.7+ JVM whereas Jetty 7 requires a 1.5+ JVM. http://www.eclipse.org/jetty/documentation/current/what-jetty-version.html. I assume that's acceptable?

I still need to sort out how to set the thread pool on the server connector. In Jetty 9 this can only be done on the constructor. There is no setThreadPool method any more. Also, I'm baffled by the https server connector. It doesn't seem possible to configure it in the same way as the http server connector. This seems to say to me that I'm not creating the https server connector correctly. But really I have no idea.

Also, if this needs to be formatted or structured differently, please let me know. I know these issues are important. I'll be happy to make those updates. Given that this is still incomplete, and I'm not sure if I've done this correctly I've decided to leave the clean-up until the end.

Thanks!