[vtkusers] vtkAppendPolyData bug

[Jeff Baumes]

> The demo seems to work fine:
>
> polydata1
> There are 2 points.
> There are 2 cells.
>
> polydata2
> There are 2 points.
> There are 0 cells.
>
> Combined
> There are 4 points.
> There are 2 cells.
>

Good. When you check in the change (you have write access now right?),
please also check in your sample code as a test in
Graphics/Testing/Cxx which fails (returns non-zero) if there are the
wrong number of points/cells. That way be can be sure it keeps
working.

Thanks,
Jeff