Jetty SPDY push improvements

After having some discussions on spdy-dev and having some experience with our current push implementation, we’ve decided to change a few things to the better.
Jetty now sends all push resources non interleaved to the client. That means that the push resources are being sent sequentially to the client one after the other.
The ReferrerPushStrategy which automatically detects which resources need to be pushed for a specific main resource. See SPDY – we push! for details. Previously we’ve just send the push resources in random order back to the client. However with the change to sequentially send the resources, it’s best to keep the order that the first browser client requested those resources. So we changed the implementation of ReferrerPushStrategy accordingly.
This all aims at improving the time needed for rendering the page in the browser by sending the data to the browser as the browser needs them.