Work around the issue of GnomeCanvasItem amending its own flags to
GtkObject::flags (which is sealed) by giving it its own flags field.
This breaks libgnomecanvas ABI and API, but I see no other way.
This commit didn't work the first time because gnome-pilot libraries
were still pulling in the system-wide libgnomecanvas, and that was
interfereing with our bundled version which has a different ABI.
But gnome-pilot integration was dropped in the previous commit, so
everything is now using the bundled libgnomecanvas.
c2c89fcb8c