[boost] [TypeErasure]_self

Hi Steven, In [docs]/type_erasure/libs/type_erasure/doc/html/boost_typeerasure/feedback.html you ask for feedback: I would be perfectly happy with _ instead of _self. You would be in sync with the folks that wrote C# Reactive Extensions (http://msdn.microsoft.com/en-us/data/gg577611) who have the convention that _ stands for "unused", which it is here, too. To me constructible<_(const std::string&)> reads fine. Markus