reduce number of test failure cases for hyperu

As was mentioned in https://github.com/scipy/scipy/pull/2909#issuecomment-24891438, there exists still a pretty large number of test cases for `hyperu` which fail. One of the reasons is the evaluation of the integral representation of `U` by means of Gauss-Legrendre quadrature which is done for `A>=0`. However, for `1>A>=0`, the integrand has an integrable divergence at zero which prevents the Gauss-Legendre quadrature from converging. I therefore propose to adjust the condition on `A` accordingly. Doing so reduces the number of failures from `737 out of 5075` to `614 out of 5058`.