I'm submitting this commit because in order to interface with the gui using an ABC block, I need to call the HostInterface.
ControlTag's only have a MovieClip* and a DisplayList& and as such lacks direct access to the movie_root that maintains the HostInterface.
DisplayObject provides the stage() function, which returns the movie_root. That function is protected, however, and cannot be referenced outside of the class/children.
In order to maintain a principle-of-least-privilage, I am opting to forward the HostInterface related functions through the DisplayObject.