[boost] [type_traits] Interest in is_iterator type trait?

Back in 2011, Howard Hinnant and I put together an is_iterator type trait based on code Howard had developed and used over a period of time. See http://beman.github.io/is_iterator/is_iterator.hpp for the actual code See http://beman.github.io/is_iterator/is_iterator_test.cpp for a test program. The intent was always to submit is_iterator to Boost, but we never got around to it. Now I need it in Boost.Filesystem, so I'd rather see it go in type traits than just sticking it into boost/filesystem/detail. If there is interest, and John Maddock gives the OK, I'll write docs and integrate into type_traits, then submit a pull request. --Beman