releasetools: Make rangelib Python 3 compatibile.

  def __ne__(self, other):

    return self.data != other.data

  def __nonzero__(self):

  def __bool__(self):

    return bool(self.data)

  # Python 2 uses __nonzero__, while Python 3 uses __bool__.

  __nonzero__ = __bool__

  def __str__(self):

    if not self.data:

      return "empty"