Follow-up to #30025: do more checks when bwc.pl resumes from a checkpoint.
Currently, bwc.pl is happy to reuse any checkpoint it finds, even if it's a rotten one. It's not absolutely dramatic in the sense that anyway this bad situation can be detected offline by bwccheck (now that we save good verification files by default). But it would be even better if verification could be done at resume time automatically.
It's no big deal. It can quite probably be done from perl fairly simply. Whether we can, and want to embark this feature inside krylov itself is less clear. (there are use cases where we do away with bwc.pl, of course, so there would be a reason for doing that).