[boost] [Concept checking] Missing TrivialIteratorConcept

Hi just occured to Sylvain Pion and myself recently that the TrivialIteratorConcept is documented but not part of the code, and same for Mutable_TrivialIteratorConcept. It is also missing from the test suite (concept_check_test.cpp) and from the archetypes. This may be intentional or not, but probably either the concepts and archetypes should be added to the code, or removed from the documentation. A small and easy bugfix for 1.32? -- Herve'