[gtkmm] Gtk::Widget: Add insert_before() and insert_after()

[Kjell Ahlstedt <kjellahl src gnome org>]

commit cc8c9e730ecb2d8e10ee0cbfad75154b2dc0adbf
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Jun 6 15:44:08 2017 +0200

    Gtk::Widget: Add insert_before() and insert_after()

 gtk/src/widget.hg |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/gtk/src/widget.hg b/gtk/src/widget.hg
index eb8ccaf..12c7aa7 100644
--- a/gtk/src/widget.hg
+++ b/gtk/src/widget.hg
@@ -516,7 +516,11 @@ public:
   _WRAP_METHOD(Widget* get_prev_sibling(), gtk_widget_get_prev_sibling)
   _WRAP_METHOD(const Widget* get_prev_sibling() const, gtk_widget_get_prev_sibling, constversion)
 
+  _WRAP_METHOD(void insert_after(Widget& parent, Widget& previous_sibling{?}), gtk_widget_insert_after)
+  _WRAP_METHOD(void insert_before(Widget& parent, Widget& next_sibling{?}), gtk_widget_insert_before)
+
   //TODO: gtk_widget_set_focus_child() is not documented. Wrap or _IGNORE?
+  // 2017-06-06: The gtk+ API is not stable yet. See https://bugzilla.gnome.org/show_bug.cgi?id=783445#c2
   //_WRAP_METHOD(void set_focus_child(Widget& child), gtk_widget_set_focus_child)
   //void unset_focus_child();
   _WRAP_METHOD(void snapshot_child(Widget& child, Snapshot& snapshot), gtk_widget_snapshot_child)