This allows you to do e.g. "hg rebase -d @ -r 'draft()'" even if some
drafts are already based off of @. You'd still need to exclude
obsolete and troubled revisions, though. We will deal with those cases
later.
Implemented by treating state[rev]==rev as "no need to rebase". I
considered adding another fake revision number like revdone=-6. That
would make the code clearer in a few places, but would add extra code
in other places.
I moved the existing test out of test-rebase-base.t and into a new
file and added more tests there, since not all are using --base.
