[CMake] Specify path to vtkIOPython for Xdmf build

[orion at cora.nwra.com]

I'm trying to build Xdmf on Fedora 8 using an updated VTK 5.1 package. 
The vtk Python libs get installed in
/usr/lib/python2.5/site-packages/vtk/.  It doesn't appear that any of the
vtk cmake files reference that location directly.  Closest I found is:

/usr/lib/vtk-5.1/VTKConfig.cmake:
SET(VTK_PYTHONPATH_DIRS
"/usr/lib/python2.5/site-packages;/usr/lib/python2.5/site-packages")

The Xdmf build fails because it doesn't know where to find the python
libraries (specifically libvtkIOPython.so).

So:

- It seems like vtk should have a variable recording where it installed
libvtkIOPython.so.

- Xdmf should make and attempt to use that variable or search for the libary.

In the short term though, how do I modify the following so the proper -L
path is addeed?

    TARGET_LINK_LIBRARIES(vtk${PROJECT_NAME}Python vtkIOPython
vtkRenderingPython vtkParallelPython Xdmf)

Thanks!

- Orion