Attached the new version of the patch which removes the resource warnings. 
Raymond, I disagree on certain points. `difflib -m` does help the development, especially for platforms where there aren't many readily available alternatives (like Windows). I gave an example for this in my first message, where you can't modify the PATH, nor install additional software. Also, you say that this should remain in tools as a demo. Wouldn't be better to have that demo well tested in stdlib and in a place where you can easy access it? This way, the user doesn't have to reimplement the wheel everytime he needs the differences between two files. And we are not competing with well developed, tested tools. By this argument, having `-m zipfile` and `-m tarfile` is redundant, because we can always use zip and tar instead.