Add support for AbstractDataLoaderService.getSessionID() utility function.
Add some javadocs to getSessionID()
Rename variable
Refactor PacketQueue.addPacket to return newly created packet.
Fix bug in PacketQueue.ack to ignore attempt to ack past acked sequence, and to
raise an exception if attempting to ack a future packet sequence.
Improve name of the test
Introduce abstract ReplicantSessionManager to simplify creation of session managers.
Use a client specific BadSessionException
Provide an implementation of GwtDataLoaderService.scheduleDataLoad()