How to add a custom icon image to a Gtk::RadioToolButton after it is created

["Douglas C. MacKenzie" <doug mobile-intelligence com>]

I have created a user interface with glade that contains
two RadioToolButtons that require custom icon images.  
I would like to compile the images into the executable
and add them to the buttons after they are created by
the glade loader.

This works fine for Gtk::Button buttons  using the set_image call.
However, the RadioToolButton class does not include the set_image
method and the Gtk::RadioToolButton method set_icon_widget()
does not appear to have any effect.

So, how do I set the image on an existing RadioToolButton?

Doug 
doug mobile-intelligence com