add full ICCCM 2.0 startup compliance

 On startup, ICCCM 2.0 compliant window managers must take ownership
 the of the WM_S%d MANAGER selection, where %d is the screen number,
 for each screen that it manages.  The selection owner window should
 be reused for the _NET_SUPPORTING_WM_CHECK window, and additional
 information should be set on that window as thought the WM was a
 normal application and this was its client leader/session leader
 window.  Information to set is:

 WM_NAME, WM_CLASS, WM_CLIENT_MACHINE, WM_COMMAND, WM_ICON_NAME,
 WM_LOCALE_NAME, WM_PROTOCOLS, _NET_SUPPORTING_WM_CHECK,
 _NET_WM_NAME, _NET_WM_PID