Integrate RPC & AutoBuffer w/h2o

AutoBuffer.close takes no args and is idempotent.
Throw AutoBufferException when the remote side prematurely closes a channel.
Strip exception nested dexceptions.
Atomically take the 1st exception to DTask
Failed parses do more cleanup
Low priority threads do not check higher-priority work queues, only the highest level system queues.
RPC supports local calls also.  Better handling of remote exceptions & canceled jobs.  Shared doAllCompletions for local & remote jobs.