* Add are_tagged_arguments_mp11 and is_argument_pack_mp11 metafunctions when Boost.MP11 is usable.
* Predicate requirements can be encoded as Boost.MP11-style quoted metafunctions as well as by MPL binary metafunction classes.
* Argument packs qualify as Boost.MP11-style lists as well as MPL sequences.
* Internal components and test programs use Boost.MP11 and C++11 type traits vice MPL and Boost.TypeTraits when Boost.MP11 is usable.