http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.4
> IconicState - The client's top-level window is iconic (whatever that
> means for this window manager). The client can assume that its
> top-level window is not viewable, its icon_window (if any) will be
> viewable and, failing that, its icon_pixmap (if any) or its
> WM_ICON_NAME will be displayed.
For these requests, we just close the window.
fixes#1279
