Single threaded IO model, intermediate commit.  Know problems with load data infile.
Merge branch 'master' into smg
Merge branch 'master' into smg
Fixed load data infile so it uses autoRead and async callbacks rather than synchronous blocking.
Split PEFuture/PEPromise into segregated interfaces for producers, async callbacks, and synchronous polling.  Changed the DBResultConsumer.writeCommandExecutor() hierarchy to stop returning (aka enabling) synchronous polling support, callers already pass in an asynchronous callback.
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Made some progress making DBConnection calls async.
Finish making typical DBConnection calls async.
Remove exceptions from signature of async calls on DBConnection, since they are required to be caught and passed to result tracker.
Convert WorkerStatement.execute() to async.
Drop unused ResponseMessage return type from WorkerRequest.executeRequest()
Made WorkerRequest.executeRequest() be async.  Known issue with kill command failing.
Made WorkerGroup.submit() asyc.  Still need to shift it to the netty thread, fix kill and any other issues.
Shifted WorkerGroup.submit() to netty thread.
Add PEContext.pushFrame(Class) method to avoid Class.getSimpleName() call if noop context is installed.
Intermediate commit.  Filling out new variable handler framework.
Clean up some comments around max_connection / max_concurrent.
Clean up some comments in various places.
Replace removed debug logging on execute success/failure
Fix issue with connection priming breaking failover tests.
Remove unused support for multiple db connection factories and pool stats.