Because this object is not functional in itself, but needs to be subclassed.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3-porting@11235 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
This simplifies the implementation of Fl_Copy_Surface and Fl_Image_Surface
which now are made to derive from Fl_Widget_Surface.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3-porting@11220 ea41ed52-d2ee-0310-a9c1-e6b18d33e121