[boost] [circular_buffer] Patch to fix two-phase name lookup issue in space_optimized

Hello Boosters, In the space_optimized circular buffer, the two calls to invalidate_iterators_except require a preceding "this->". The actual invalid_iterators_except() function is only accessible through a dependent base, so we need to make the invalid_iterators_except name dependent. The DEC compiler tried to tell us this at one point, but we ignored it. Patch is attached. - Doug