[boost] [math] pull request for boost::math::round bug in corner cases

Hello, I found two corner cases in which boost::math::round doesn't round correctly. For double types, these are the numbers directly beneath 0.5: +/- 0.499999999999999944488848768742172978818416595458984375 (which get rounded to 1.0 although their aboslute value is smaller than 0.59) and odd integral numbers on the edge of the mantissa length: +/- 4503599627370497.0 +/- 4503599627370499.0 +/- 4503599627370501.0 ... +/- 9007199254740989.0 +/- 9007199254740991.0 +/- 9007199254740993.0 These get rounded to the next bigger/smaller integral value. For a detailed explanation and a fix, see the description of the pull request on https://github.com/boostorg/math/pull/8 Regards, Robin