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".
end of Time::operator++. This allows to know if the next timeIndex will be
a dumping time. The function object "partialWrite" modifyes the write option
of the those fields which will be written down at given intervals of the overall
outout times.
