* compare baseline to 1.2.6

* remove the entire concept of the completion manager; it just doesn't make sense any more; everything async and external facing should be via the TP

* use "in" with ForAwait to avoid some extra copies

* experimental "backlog queue" approach

* Cleanup and de-dupe timeout exception data

* WriteMessageTakingWriteLockSync should consider backlog

* don't allocate all those strings