Fix msvc build.
Revert "Fix msvc build."

This reverts commit 26c5a1f7b73c913b9b11f89bc8ff48c8605ad229.
Merge branch 'master' of https://github.com/BoostGSoC/boost.math
Get gamma.hpp compiling with msvc.
Merge branch 'master' of https://github.com/BoostGSoC/boost.math

Conflicts:
	boost/math/special_functions/gamma.hpp