[vtkusers] vtkHexagonalPrism and vtkPentagonalPrism

[Mathieu Malaterre]

Hi all,
	I made some fearly big changes to those two classes:

- vtkHexagonalPrism and
- vtkPentagonalPrism

	I did run some simple tests on it to check if the results were still 
right. But I would appreciate if people could report any major issue 
such as:
- speed
- wrong interpolation value (contour / clipping)
- crash / seg fault

Thanks for your attention,
Mathieu