Handle WM_CHANGE_STATE requests for iconic state

Handle WM_CHANGE_STATE requests for iconic state

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