* x11/x11_display.cpp: the "parent" window now receive structure

  * x11/x11_display.cpp: the "parent" window now receive structure
    notify events
  * x11/x11_window.cpp: same thing for the other windows
  * x11/x11_loop.cpp: when the "parent" window receives a map notify event,
    we show all the windows because it doesn't seem to be automatic.
    To have this working, we must update the visibility variable of the
    windows when they are hidden by the window manager