gdkwindow: ignore shape on client-side windows when recomputing visible regions

Rendering doesn't do much about clipping drawing operations to the window shape,
although invalidation applies the shape to every window, leaving possibly trails
of "overrendered" content. So ensure the shape portions get invalidated too when
the window is moved/resized.

https://bugzilla.gnome.org/show_bug.cgi?id=729095

gdk/gdkwindow.c

@@ -935,7 +935,7 @@ recompute_visible_regions_internal (GdkWindow *private,
 	  /* Convert from parent coords to window coords */
 	  cairo_region_translate (new_clip, -private->x, -private->y);
 
-	  if (private->shape)
+	  if (should_apply_clip_as_shape (private) && private->shape)
 	    cairo_region_intersect (new_clip, private->shape);
 	}
       else