Fix regression in :class:`fractions.Fraction` if the numerator and/or the
denominator is an :class:`int` subclass. The :func:`math.gcd` function is now
used to normalize the *numerator* and *denominator*. :func:`math.gcd` always
return a :class:`int` type. Previously, the GCD type depended on *numerator*
and *denominator*.
