void gdk_window_lower ( GdkWindow* window )
window to the bottom of the Z-order (stacking order), so that
other windows with the same parent window appear above
This is true whether or not the other windows are visible.
window is a toplevel, the window manager may choose to deny the
request to move the window in the Z-order,
requests the restack, does not guarantee it.
gdk_window_show() raises the window again, so don’t call this
function before gdk_window_show(). (Try gdk_window_show_unraised().)