The horizontal variants are gone from the API.
gtk_rc_get_theme_dir has been deprecated, there is
no replacement so we do the equivalent lookup.
Right-aligned menu items are deprecated.
For now defining gtk_widget_render_icon and
gtk_widget_set_size_request gets rid of warnings.
There is only GtkBox, neither GtkHBox nor GtkVBox.
Constructors and defaults have changed, we need
to set "orientation" for vertical boxes.
The panel takes care of its pages, and the view
of itself.
gtk_container_add on GtkBox is different to GtkVBox
so we must use gtk_box_pack_start.
GtkScrollable exists as a proper interface now.
