Reimplementing or removing children() in gtkmm 3

[Murray Cumming <murrayc murrayc com>]

GTK+ 3 will remove many struct fields that we were previously able to
(and maybe meant to) access directly. This includes, for instance,
GtkBox::children, which is already marked with GSEAL, allowing us to
experience the pain today if we choose:
  http://git.gnome.org/browse/gtk+/tree/gtk/gtkbox.h#n58
But we use this to implement our STL-style API, via
Gtk::Box::children().

So we need to either
- Find a way to do this without the struct field
or
- Remove that API from gtkmm.


It would be great if someone wants to look at the problem.

I try to keep the gtkmm-3maybe branch from using any deprecated API, so
to see the problem, checkout the glibmm3-maybe branch, 
comment out the 
  #undef GSEAL_ENABLE
here:
  http://git.gnome.org/browse/gtkmm/tree/gtk/src/box.hg?h=gtkmm-3maybe
then build with 
./autogen.sh --enable-warnings=fatal


-- 
murrayc murrayc com
www.murrayc.com
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