Some format upgrade/downgrades -needs- revlog to be recomputed. So we now
detect that individually and warn when it contradict explicitly passed flag.
This is part of a larger series to make debugupgraderepo smarter about which
revlog it picks by default.
I think it would be simpler (and technically faster even though it most likely doesn't matter here) to say if not specified_revlogs.get(FL) (same for the other two similar places)