Order of archives on index page is not stable
Packages like mock provide equivalent zips and tarballs for each release, and pip simply downloads the first one on the index page. When we attack https://github.com/pypa/pip/issues/1175, it will be helpful if pip chooses the same archive (for a given platform) every time. Otherwise, when pip hands the user the hashes of downloaded archives, it will have to give one for each format, which means downloading them all. However, at the moment, there is no ORDER BY clause on the query PyPI uses to list the downloads. We should order by something stable and unique, like the archive file name.