BUG-413812

Mark RateTracker as Serializable to allow it to be stored in a Session that is
eventually persisted in a distributed memory platform.

Signed-off-by: David Harrigan <dharrigan@gmail.com>
Merge branch 'jetty-7' into jetty-8
Merge branch 'jetty-8'
Fixed method parseResponse() that should never return null.

The response is "filled" by parser events even if at the end of
the parsing the parser returns false.
Merged branch 'master' into 'jetty-9.1'.