nested trees design-approach : composite trees vs iter_changes

[Ian Clatworthy]

Robert Collins wrote:
> I think users (which includes us) that write to the API will see most of
> the things I enumerated bite them repeatedly. Its worth noting that such
> users include sysadmins doing precommit hooks, integration into
> buildbots and other such tasks.
I'd still like to see a concrete, practical example. You mentioned
Tree.add() in your original email but I can't think of when I'd ever
want to call that in a precommit hook.

Ian C.