[gtkmm] using a stock pixmap in a button

[Tim Flechtner <timf trdlnk com>]

i apologize if this is documented some place obvious, but i've looked, 
and i can't figure out how to set up a button to use a stock pixmap (i 
want to change the pixmap and label of a button at runtime).  can anyone 
point me to documentation or provide an example?

thanks!
-tim