Add Jetty HTTP client

[thboileau]

Initial ticket : http://restlet.tigris.org/issues/show_bug.cgi?id=653

[jlouvel]

Tal has contributed this client here:
https://github.com/tliron/restlet-jetty9

To be merged for RF 3.0

[jlouvel]

Set milestone to 3.0 M1 which will require Java 7.

[jlouvel]

See related issue #793

[jlouvel]

Closing for now. Issue #793 stay open due to remaining SPDY and test cases items.