This modified version of a patch by Thomas Heller allows __import__

This modified version of a patch by Thomas Heller allows __import__
hooks to take over the Python import machinery at a very early stage
in the Python startup phase.

If there are still places in the Python interpreter which need to
bypass the __import__ hook, these places must now use
PyImport_ImportModuleEx() instead. So far no other places than in
the import mechanism itself have been identified.