I really wish one can reply to comments like in email, by quoting part of original mail. I don't know if the new tracker allows such option. Coming to the point,

1) MOVEFILE_COPY_ALLOWED is not needed to fix 1693753 but is needed if old functionality needs to be maintained. The API MoveFile() does move files across file systems (as per msdn doc).

2) As per os.rename doc, renaming across file systems *may* fail on some unix flavors. That gave me the impression that it *may* succeed on some others. If we can confirm that it *always* fails on *all* flavors, we can update the doc and I can do away with MOVEFILE_COPY_ALLOWED.

3) The patch breaks exiting code behaviour as jorend noted but not patching for that reason alone does not seem right to me, particularly since the patch adds desirable functionality. I don't think coming up with a new function name is a good idea. Is it ok to change the behaviour  of rename() based on some setting in "os" module? If nothing else, the patch can be applied to 3.0 and 2.x users can be given warnings.