Fix Resolver shutdown behaviour

* Add Resolver prefix to logging.
* Fix AsyncObject::removeReference() logic.
* Fix work remaining logic.

I spotted this while playing around with Application Stoppable behaviour. 
Reviewers: @nikb @vinniefalco 
@HowardHinnant You advocate action ("we should probably go with lambdas"). I'm requesting more detail on the precondition for the action you advocate ("In cases where both...work equally well").