gfio: use appropriate gtk signal for draw/expose of graphs

draw on gtk3, expose_event on gtk2.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/gcompat.h b/gcompat.h
index 66fb781..cd9602f 100644
--- a/gcompat.h
+++ b/gcompat.h
@@ -29,4 +29,10 @@
 guint gtk_widget_get_allocated_height(GtkWidget *w);
 #endif
 
+#if GTK_MAJOR_VERSION == 3
+#define GFIO_DRAW_EVENT		"draw"
+#elif GTK_MAJOR_VERSION == 2
+#define GFIO_DRAW_EVENT		"expose_event"
+#endif
+
 #endif