Need to move more intelligence into bundler

[Sune Foldager]

Benoit, I think we're gonna have to move even more intelligence into the bundler.
Currently, group performs the main revision loop, and calls the bundler to generate
each revision entry in the bundle.

I think we'll need to move the loop into the bundler as well. In that way, the
bundler can have maximum flexibility to select deltaparents and to ask the revlog
what deltaparents IT uses, so it might strive to use the same, so the deltas can be
transfered directly. It can also test that it actually includes, in the bundle, the
revisions it would base against, which is important.

It would presumably no longer need to call revdiff, or at least not until it has
already called deltaparent and perfomed some decisions.

I am of course thinking of the scenario bundle2 + generaldelta/lwcopy here.
What do you think?

Sune