Rather than requiring each functionObject to handle failed construction
internally (using the active_ flag) the static member function "viable"
is provided which returns true if construction of the functionObject is
likely to be successful. Failed construction is then handled by the
wrapper-class which constructs the functionObject,
e.g. "OutputFilterFunctionObject".
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.
