[boost] hash_fwd dependency (Was: New dependency report)

Antony Polukhin wrote:

Would it be good to move a single header into the Boost.Core? This header depends only on Boost.Config. It adds dependency to a whole Boost.Functional library for the following libraries: array, container, filesystem, multiindex, thread, type_index, variant.

While the general subject of forwarding headers still deserves consideration, in this specific case I wonder if moving funcional/hash into its own 'hash' module would not alleviate most of the problem. I know that std::hash is in <functional>, but it still feels wrong having boost::hash in boost/functional/hash.hpp.