For ENG-5088, fix some bugs in PersistentBinaryDeque and StreamBlockQueue

Stream block queue wasn't handling the scenario where some persisted buffers were pulled out of the PBD and then the in-memory buffers had to be synced.

The PBD was also not maintaining internal state correctly about what buffer to return next. We'll know more once we have the system tests running.
For ENG-5088, remove a debug print statement
For ENG-5088, do some cleanup based on Ning's feedback
For ENG-5088, actually do need to increment the poll segment index to catch the write segment
Merge pull request #725 from VoltDB/ENG-5088

For ENG-5088, fix some bugs in PersistentBinaryDeque and StreamBlockQueu...