This patch includes a new FindPythonLibs.cmake that uses the python
patchlevel header to generate PYTHON_VERSION variables for CMake, so
that CMake scripts know what version of python is being used.  It also
adds a vtkPythonConfigure.h file that includes these variables, so
that source files can check the python version before Python.h is
included.  This feature is used to avoid macro conflicts between
Python.h and other header files included by VTK.

Change-Id: I7c52e96cf5b3bf48e7c227e8d9ceae44671ae908