Catching window.destroy

[Jon Harrop <jon ffconsultancy com>]

When a user clicks on the "X" of the main window of my GTK app, I'd like to 
handle the signal (e.g. to check for unsaved data). How do I handle this 
signal to prevent the window from disappearing?

Many thanks,
-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e