Added comments on Rietveld. But I'm not sure that this change is worth to do. Only low-level functions in os.path and os modules (and few other) support bytes names (and only bytes, not bytearray!). High level interfaces, such as in tarfile or zipfile, work only with str paths. The question is what level the tempfile module?

In any way Mercurial people need their own wrapper if they want to support Python <3.5.