[me]
> You must not have noticed Session.is_empty(), which is the same as your
> is_dirty() only of the opposite sense:

[Jon]
> Not true, actually. is_empty() says there's nothing of interest in the
> session object; is_dirty() says that what's in the session object does not
> match what's in the persistent store.

Yes, I noticed that shortly after posting.  Fixed by changing how
is_empty() is interpreted -- it has now been replaced by is_dirty().
The docs shrank by a sentence, so that must have been the right
solution.  ;-)

        Greg