Code review comment for lp:~javier.collado/checkbox/bug990075

Since the time this branch was first proposed for merging, the trunk has been converted to Python 3. I've just noticed that this branch uses the cmp keyword argument to the sorted function, which is no longer supported in Python 3. And, there might be other constructs that are no longer supported. So, I'm setting this branch as "Needs Fixing" just so that it's at least tested against Python 3 before being resubmitted.