DRILL-4134: Allocator Improvements
- make Allocator mostly lockless
- change BaseAllocator maps to direct references
- add documentation around memory management model
- move transfer and ownership methods to DrillBuf
- Improve debug messaging.
- Fix/revert sort changes
- Remove unused fragment limit flag
- Add time to HistoricalLog events
- Remove reservation amount from RootAllocator constructor (since not allowed)
- Fix concurrency issue where allocator is closing at same moment as incoming batch transfer, causing leaked memory and/or query failure.
- Add new AutoCloseables.close(Iterable<AutoCloseable>)
- Remove extraneous DataResponseHandler and Impl (and update TestBitRpc to use smarter mock of FragmentManager)
- Remove the concept of poison pill record batches, using instead FragmentContext.isOverMemoryLimit()
- Update incoming data batches so that they are transferred under protection of a close lock
- Improve field names in IncomingBuffers and move synchronization to collectors as opposed to IncomingBuffers (also change decrementing to decrementToZero rather than two part check).
This closes #238.
