[gtkmm] error compiling examples

["xavier dufresne" <xdufresne gmx fr>]

I commited a bug yesterday evening (error compiling examples), and sent a
patch this afternoon and set the bug as FIXED.
It's the first time I commit a bug and submit a patch, so I don't know if I
did it the right way.

I think someone should check it.

Thank you

xavier