Code review comment for lp:~spiv/bzr/just-add-repr-687653-2.2

This is a nice minimal fix for 2.2, and apparently fixes the issue in production.

I think generally we shouldn't have any objects doing real work from their str or repr method, and exceptions should be a lot like value objects.

Perhaps we should have an optional ".hint()" method that the ui can call.

I am kind of inclined to delete this in trunk but it's not really a priority.