Looks fine. Can you check this in yourself?

Nit: I note that the line added for _fileio to PC/config.c is improperly indented (space/tab issue?).

Note that this will make various tests using f.truncate() fail.  At some point we need to implement it using the same APIs as were used in the old file object.

Also, my hope is that eventually we'll have a Windows specific version of _fileio.c instead of this code, using all-native Windows API calls.  (Any volunteers?)