This function's purpose is to handle these special cases of argv[0]:
* Invoked using python -m ...
* Invoked using a path to the executable even though the executable is
   on the PATH

This change enhances the path comparison to support normalization of
that path, Windows long path prefixes, and also the easy-install
behavior on Windows where argv[0] has no extension.

Yet to be properly handled is invocation using python -c ...