TODO
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Make gnome-stroke-draw.c:gstroke_invisible_window_init (GtkWidget *widget) 
use Gtk+ primitives, not X11 primitives (no idea if this is even possible). 

Should the static vars gstroke_* in gnome_stroke_draw.c be moved to
stroke_metrics structure?

Improve the autoconf macros. They should probably use the gnome
autoconf infrastructure. Help with this would be appreciated.