a GTK.TearoffMenuItem is a special W(MenuItem) which is used to
tear off and reattach its menu.
When its menu is shown normally, the GTK.TearoffMenuItem is drawn
as a dotted line indicating that the menu can be torn
off. Activating it causes its menu to be torn off and displayed in
its own window as a tearoff menu.
When its menu is shown as a tearoff menu, the GTK.TearoffMenuItem
is drawn as a dotted line which has a left pointing arrow graphic
indicating that the tearoff menu can be reattached. Activating it
will erase the tearoff menu window.
GTK.TearoffMenuItem()->set_usize( 100,0 )
GTK.Table()->set_row_spacings()