[vtkusers] vtk's wx namespace collides with wx's wx

[Torsten Sadowski]

Hi,

after installing vtk I couldn't use my wxPython (2.5) anymore. The reason
was the wx subdir in vtk_python which by importing overwrote the whole wx
namespace which obviously does break some bits. Renaming the dir to wxvtk
solved the issue.

Torsten