Fix for issue #927

[mborland]

Return -INF or +INF if the result is INF rather than throwing an overflow exception.

[jzmaddock]

I think this is the wrong fix - and actually we are doing exactly what we promised to do here.

If you want the sign of the infinity rather than an exception, then use a Policy which ignores overflow errors and you will get a signed infinity back.

[mborland]

What is the appropriate policy to use here to get the signed infinity?

[jzmaddock]

If it's project wide then

#define BOOST_MATH_OVERFLOW_ERROR_POLICY ignore_error

or

#define BOOST_MATH_OVERFLOW_ERROR_POLICY errno_on_error

Depending on whether you want to be able to check errno for overflow.

If it's just this function, then:

using namespace boost::math::policies;

boost::math::specfun(arg, make_policy(overflow_error<errno_on_error>()));