[master] Remove Iterable implementation from BufferPool.  It was present for testing purposes only.   Reworked test logic to not depend on it.
[master] don't create DecisionListener every time
[master] + avoid generating HttpContent.Builder objects
[master] + avoid generating Transport.FlushEvent objects
[master] + fix copyrights
[master] + avoid creating Read/WriteResult Objects every time we call CompletionHandler
[master] + minor cleanup