[boost] [config] BOOST_NO_CXX11_HDR_CODECVT is not defined for VC14

Hi, I see that BOOST_NO_CXX11_HDR_CODECVT is not defined for MSVC-14, although it is known that the codecvt facets are unusable because of linkin errors: https://connect.microsoft.com/VisualStudio/feedback/details/1348277/link-err... You can also see STL mentioning DevDiv#1060849 here: http://blogs.msdn.com/b/vcblog/archive/2014/11/12/visual-studio-2015-preview... and I can see that the problem is not fixed in RTM. This also concerns std::codecvt specializations for char16_t and char32_t. Can we define the BOOST_NO_CXX11_HDR_CODECVT macro for MSVC?