[gtkmm] Using derived classes with libglademm

[Rob Benton <rob benton conwaycorp net>]

(I don't know if this is the right list for this question.  If not
please direct me to the right place.)

If I want to create my main window to be a derived class of Gtk::Window,
how can I get glade/libglademm to do this?  I'm unable to change the
class property in the dialogs.