untested code adding support for console monitor through an OutputStream decorator.
Code is quite clear, excepted the maybeWrite method which (to my mind) shouldn't consume many CPU cycles to obtain some cool log writings.
Of course it bypass Wagon transfer logging mechanisms, but I remove the Wagon here, so there is some kind of coherence.
Did you know that commons-io already contains such formatting code ? Me neither, but StackOverflow did : http://stackoverflow.com/a/4888400/15619