gcompat: gtk_widget_get_window() for below 2.14

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/gcompat.h b/gcompat.h
index cd9602f..61b9894 100644
--- a/gcompat.h
+++ b/gcompat.h
@@ -22,6 +22,10 @@
 {
 	return dialog->vbox;
 }
+static inline GdkWindow *gtk_widget_get_window(GtkWidget *w)
+{
+	return w->window;
+}
 #endif
 
 #if GTK_MAJOR_VERSION < 3