[vtkusers] vtkHardwareSelection produces bad a bad result

[David E DeMarle]

> There might be some sort of topological walk algorithm that would produce
> an exact result but I am not aware of one and suspect that it will be orders
> of magnitude slower than the rendering based algorithm we have now. A
> frustum selection will produce an exact result and do it fairly quickly, but
> it does not and can not determine which cells are visible and which are not.
>

Frustum followed by a back face removal (remove cells who's normals don't
face toward the camera) would likely be faster than a topological walk and
nearly correct, but it will fail for instance on objects with holes.
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