Inclusion List for Bert Tree

[Marc Stiegler <marcs>]

Hugh and I discussed approximately this same idea some months ago as a
quick and reasonably painless bert representation. We rejected because,
though there are a lot of similarities between the needs of the bert
tree and the behavior of the inclusion list, there are enough differences
to make it ill-suited. We should have a meeting on this if you're really
enthusiastic about it; email doesn't have enough bandwidth.

My current preference is bob's recommendation to have Trace Backward 
and Trace Forward rather than Revert and Revert Forward. This would
be combined with another idea of dean's, for accessing old versions
through a popup Time menu from the control panel, which people can
see in the next release of the frontend documentation.

--marcs