Gtk::LayoutManager::allocate_vfunc has extra const
The virtual function Gtk::LayoutManager::allocate_vfunc()
is declared as
virtual void allocate_vfunc(const Widget& widget, int width, int height, int baseline);
in which widget
is passed by const reference. This defeats the point of that function, because its purpose is to allocate widget
and its children, which requires it to be non-const. The const
is not present in the C API, and should be removed here.