Boost-Extras: Helpers to use boost::intrusive_ptr<>

This is a start, a helper to use boost::intrusive_ptr<> with objects reference counted. This is very helpful for a largescale project, especially if you already have pointers all over the place and cannot find that leak... Reference counted pointers will help you a lot. With these, you can pass bare pointers around and still save them in an intrusive_ptr<> (or smart pointer) and it will just work.

Note: If you start a new project, you may want to look into use boost::shared_ptr<> instead!