[boost] intrusive_ptr wrapper for C++/CLI

I do a lot of development using native C++ and managed C++/CLI, and have coded a simple smart pointer wrapper around intrusive_ptr to allow C++/CLI code to use reference counting objects without change. IntrusivePtr takes advantage of the template support engineered for gcroot<T> to implement the smart pointer. It’s a wrapper to support factory functions that return intrusive_ptr. Whilst many would object to putting C++/CLI conditional code into boost, the smart pointer is too small to stand alone and too boost specific for Microsoft. thoughts welcome https://ql.codeplex.com/SourceControl/latest#IntrusivePtr/boost/IntrusivePtr...