[boost] [type_traits] is_base_of<B, D> should work when B is incomplete

Hi, I have filed the following ticket: https://svn.boost.org/trac/boost/ticket/12027 The Standard ([meta.rel]) requires that in std::is_base_of D must be a complete type, but it does not require the same of B. This makes sense, because if we compare a complete type D and an incomplete type B, the former is surely not derived from the latter. In contrast, boost::is_base_of imposes an additional constraint that B must also be complete. Could this restriction be lifted? Regards, &rzej