Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1921
Avoids the clutter and maintenance effort associated with providing the function signature string.
This had been used in functionObjects: Info(log)<< "messages" << data << .... in which it is not at all clear what the "log" argument does whereas if (log) Info<< "messages" << data << .... is totally clear and more efficient.