gtk-clist-append does not work with shared substrings

["Greg J. Badros" <gjb at cs dot washington dot edu>]

Whereas this works:
;; (gtk-clist-append clist (list "foo" "bar"))

This does not:

;; (gtk-clist-append clist (list (make-shared-substring "foo") "bar"))

Also, I don't think there's any way to tell which version of guile-gtk
you're linked against.  `guile-gtk-version' is a nice primitive to add.

Thanks,
Greg