[boost] [type_traits] Another big update in develop

Just a heads up in case it causes any issues: type_traits has had another big update in develop - added several new traits is_constructible, is_assignable etc which were needed to fix bugs in other traits - and changed most of the has_nothrow and has_trivial traits to make use of these. Also added more test cases to cover the issues where these were defective before. Please do let me know if you spot any unexpected breakages. John.