Message 296690 - Python tracker

My commit c8fb58bd7917151e63398587a7fc2126db7c26de (co-written with Jeremy Kloth) fixes the "macro redefinition".

There are still warnings in the siphash code, but I suggest to report them upstream, and *then* propose to cherry-pick fixes from libexpat (as I did for Visual Studio 2008 support in Python 2.7 when I upgraded libexpat to 2.2.1, but I was lucky, the fix was already made in libexpat).