400434 - Add support for an OutputStream ContentProvider.
400631 - Calling flush() on HttpServletResponse.getOutputStream() after last byte of body causes EofException.

Now flush() is a no-operation if the stream is already closed, consistently with previous Jetty versions.
362854 - Continuation implementations may deadlock.

HttpChannelState was already notifying listeners from outside synchronized blocks,
apart one case, in expired().
Also taken the chance to cleanup the class from warnings.
Merge branch 'master' into javawebsocket-jsr
393473 - Add support for JSR-356 (javax.websocket) draft

 + Refactoring EventDriver to be more pluggable (for jsr endpoints)