fails:Rational#** when passed Rational converts self to a Float and returns it raised to the passed argument
fails:Rational#** when passed Rational returns NaN when self is negative and the passed argument is not 0
fails:Rational#** returns Infinity for Rational(0, 1) passed a negative Rational
fails:Rational#** when passed Bignum returns Rational(-1) when self is Rational(-1) and the exponent is odd
