Signal for changed checkboxes with SimpleList column type bool?

[Martin Junius <mj+gnome ml m-j-s net>]

Dear list,

I'm using SimpleList with column type bool to get a column with 
checkboxes, which works as expected. Now I want to trigger a callback 
when any of the checkboxes are changed. What signal must be connected 
and how?

As always, thanks in advance for your help.

Martin