debugcommands: add a `--paranoid` option to `debug-repair-issue-6528` See justification inline. Differential Revision: https://phab.mercurial-scm.org/D11263

repair: improve performance of detection of revisions affected by issue6528 Explanations inside the patch. I've tested this on Mozilla-Central and it's 5 times faster than the naive approach on my laptop. Differential Revision: https://phab.mercurial-scm.org/D11262

debugcommands: introduce a debug command to repair repos affected by issue6528 This command is quite basic and slow, it will loop over the entirety of the filelogs in the repository and check each revision for corruption, then fixes the affected filelogs. It takes under 25 minutes for Mozilla-Central on my not-top-of-the-line laptop, using the `--to-report` and `--from-report` options will make this pretty tolerable to use, I think. This change also introduces a test for the fix. Differential Revision: https://phab.mercurial-scm.org/D11239