The original problem seems to come from some Unix platform, but this
patch only handles two cases:
- on win32, when the argument is a bytestring.
- on OS/2.
And in both cases, the default (utf-8) conversion seems wrong. Something
like cp1252 (the ANSI code page for Western Windows) would be more sensible.

In the posix part of the function, there is the comment (2003-03-04):
    /* fall back to the original byte string, as
       discussed in patch #683592 */
btw, I find the penultimate message of this other thread very pleasant,
in the py3k context... I suppose the conclusions would not be the same
today.