See 56d3e0b499df for the source of adding originalwd to the list of things that
cause wdir to be updated. That change didn't come with tests, and attempts to
recreate the scenario described have thus far failed.
I'm not real familiar with how rebase works, and seems like it's pretty intricate code. I'd also feel better if there were tests for the original commit referenced. But it's very unlikely that I'll have any time before the weekend to look at this again, so I thought I'd send it out now. Maybe it's narrow enough or maybe somebody can backfill the tests, and we can avoid a known data shredder in the next release.