When this class creates an object, it sets the object's embedded
Gadget.Width and Gadget.Height fields according to the frame image in
GA_Image.  If the GA_Image understands the IM_FRAMEBOX method, the gadget
asks the GA_Image what it dimensions would be if it had to surround the
display element.  If the GA_Image does not support IM_FRAMEBOX, it just
copies the GA_Image image's width and height into the Gadget structure.