fix besselj, expint, gammainc, erf, erfc for fp by falling back to the generic code by default
fix besselj, expint, gammainc, erf, erfc for fp by falling back to the generic code by default

klkuhlm/mpmath,JensGrabner/mpmath,bjodah/mpmath,bjodah/mpmath,JensGrabner/mpmath,klkuhlm/mpmath,fredrik-johansson/mpmath