version string.

    If you have a version string that isn't rational (i.e. NormalizedVersion
    doesn't like it) then you might be able to get an equivalent (or close)
    rational version from this function.

    This does a number of simple normalizations to the given string, based
    on observation of versions currently in use on PyPI. Given a dump of
    those version during PyCon 2009, 4287 of them:
    - 2312 (53.93%) match NormalizedVersion without change
      with the automatic suggestion
    - 3474 (81.04%) match when using this suggestion method

    @param s {str} An irrational version string.
    @returns A rational version string, or None, if couldn't determine one.
    ))