Using Gtk::Grid in gtkmm-documentation

[Murray Cumming <murrayc murrayc com>]

The latest unstable version of GTK+ deprecates GtkBox, so we should
replace it with Gtk::Grid in the gtkmm book's examples. Does someone
have time to do that?
http://git.gnome.org/browse/gtkmm-documentation

You will know that it's done when you can build gtkmm-documentation with
the --enable-warnings=fatal configure option.

(By the way, I will soon take a day to go through the various
outstanding patches for gtkmm, libsigc++, etc and deal with them
properly.)

-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com
www.openismus.com