[vtkusers] How do I reset vtkProcessObject inputs to NULL?

[Dean Inglis]

In my app, I load in a large data file to a reader which
checks for an abort signal on user command during reader->Update().
That is, the reader has had
    reader->SetStartMethod(&BeginGauge ,static_cast<void*>(this));
    reader->SetEndMethod(&EndGauge ,static_cast<void*>(this));
    reader->SetProgressMethod(&UpdateProgress ,static_cast<void*>(this));

with a check and flag for abort in the ProgressMethod. In the case of an
abort, I would like to reset the reader so that any prior completed inputs
(i.e. reader->Update() was successful) are removed and the reader is 'reset'
to an un-initialized status.  Do I also need to reset all downstream members
of the pipeline, i.e. any filters:
   filter->SetInut(reader->GetOuptut());
with
   filter->SetInut(NULL);
?

What are the correct methods/setup to do this?

Dean