[boost] Boost.Locale will require C++11

Quick announcement: I'm planning on dropping C++98 support for Boost.Locale. I.e. require e.g. Rvalue references and std::unique_ptr to reduce maintenance effort. If anyone knows a reason to not do that please respond to https://github.com/boostorg/locale/issues/90 As per suggestion from Peter I'll add a warning for the upcoming release and will drop support in the next if there isn't anything in particular. Especially recent ICU headers already requiring C++11 is enough of a reason to not stick to the old stuff. Regards