window.c: Use frame code for drawing menus

This gives us a nice frame and drop shadows for the menus.
diff --git a/shared/cairo-util.h b/shared/cairo-util.h
index d679bcb..a8eb874 100644
--- a/shared/cairo-util.h
+++ b/shared/cairo-util.h
@@ -64,6 +64,8 @@
 };
 
 void
+theme_set_background_source(struct theme *t, cairo_t *cr, uint32_t flags);
+void
 theme_render_frame(struct theme *t, 
 		   cairo_t *cr, int width, int height,
 		   const char *title, uint32_t flags);