RpcDispatcher/MessageDispatcher: additional methods which return a Future rather than blocking

Currently, synchronous (cluster-wide) calls in RpcDispatcher and MessageDispatcher block until all (or a portion) of the responses have been received.
Goal: to provide additional methods for callRemoteMethods() and castMessage() which return a Future<RspList>. This allows a user to dispatch multiple blocking calls and fetch the result later, e.g. (pseudo code):

Future<RspList> r1, r2;
r1=dispatcher.callRemoteMethods(null, "foo", new Object[]

{10}, new Class[](int.class}, GroupRequest.GET_ALL, 5000);
r2=dispatcher.callRemoteMethods(null, "bar", new Object[]{10}

, new Class[](int.class}, GroupRequest.GET_ALL, 5000);

// do something
if(r1.isDone()) {
RspList rsp_1=r1.getResult();
}

This should be combined with a notification mechanism (RspFilter) so a users gets notified (if desired) of each response, and also when the result is complete