os independent rename

[Lee Harr]

I just got a bug report the heart of which is the
difference between unix and windows in using
os.rename

(ie, "On Windows, if dst already exists, OSError will be raised")

Hmm, I thought, maybe I'm supposed to use
shutil here. That is the "high-level" operations.
Unfortunately, shutil.move says it depends on
os.rename

So, what is the best way to do this that will
behave the same across operating systems?