[boost] [iterators] Missing typedefs in v1.57

I posted this a week ago in the user mailing list but it went unnoticed. Perhaps this developers' list is a better place to post it. The typedefs for difference_type and reference used to be in scope for classes derived from iterator_facade. Since v1.57 they have to be declared thus: typedef typename iterator_facade_::difference_type difference_type; typedef typename iterator_facade_::reference reference; This seems out of place for a class that was designed to reduce boiler plate code. However, if the change was intentional, please document it. Thanks, Keith MacDonald