This makes it possible for the Asynchronous listener to get the
messages. It can then process them in a more fancy way.
The default implementation will still log the messages to the console
(if debug is enabled), but it will do so from the Async listener for
asynchronous requests now. This means they will probably be logged from
the same thread, and show up in a more readable way.
This also makes it possible to listen to several requests and log them
in a nice way (in a status window or whatever).
ed31589c37