Launcher does not use application's requested default icon

The icon defined in 'gtk_windows_set_default_icon' is not rendered on the Unity launcher. Instead it keeps displaying the icon as defined in the .desktop file.

This is different to the behaviour of e.g. the GNOME panel and other launchers where the windows icon is updated. This can nicely be used for displaying a program's state or for drawing user's attention to the application if it runs iconified (with the advantage of avoiding any additional icons in the panel).