[boost] A few more critical dependencies

At present, we have three dependencies that we can easily cut and doing so will be very beneficial: 1. type_traits now depends on utility only because utility: from from from from from Since declval.hpp itself depends on type_traits (add_rvalue_reference), it can't go to core and the most logical place for it is type_traits itself. 2. utility depends on iterator because iterator: from from boost/iterator.hpp can be moved to core in all its former glory (and probably replaced by a one-liner, using std::iterator.) generator_iterator.hpp perhaps needs to be moved to iterator. 3. mpl depends on detail because detail: from from That last one is just because lightweight_test.hpp hasn't been removed from Detail yet; let me know if I should do that. boost/detail/endian.hpp is just a forwarding header that includes . We should move it to Predef. Comments? Objections?