[vtkusers] Disable warning about "does not support stereo"

[David Cole]

> it would be called from
> vtkInteractorStyle::OnChar()
>
> You may subclass vtkInteractorStyle you use -
>
> (for example vtkInteractorStyleTrackballCamera ), override
>  virtual void OnChar();


If you are overriding OnChar, simply do not call the parent class when 
the '3' key is pressed. The '3' key means "turn on (or off) 3D stereo 
viewing" in the default interactor style. And attempting to do that is 
what triggers the warning...

Search for "Keypress 3" here:

    http://www.vtk.org/doc/nightly/html/classvtkInteractorStyle.html


HTH,
David