Instead of finding Python interpreter, library and framework on Mac,
rely upon the reported paths of the interpreter (executable) to decipher
whether a framework is being used, then ensure any such framework has
its versioned subdirectory Headers used for includes and the base
Python library used directly in linking. This removes ambiguity in
framework searching, allowing just the PYTHON_EXECUTABLE (user-defined
or from FindPythonInterp module) to control which Python is used.
5df9cbc964