lib updates (in particular, see https://github.com/aspnet/KestrelHttpServer/issues/2694#issuecomment-420347853)

* make transaction inner tasks use RunContinuationsAsynchronously (for discussion, see issue #943); detect RunContinuationsAsynchronously in ResultBox completion, and set directly rather than deferred

We decided this won't help anyone long-term, as the signature to types still differs. With strong naming you *could* load both as a workaround, but the upgrade cutover has to happen at some point and this does it for the 2.0 release.