This should be faster and more future-proof. Calls where the result is to be
sorted using util.sort() have been left unchanged. Calls to .items() on
configparser objects have been left as-is, too.
- simplify finding first bad rev
- no need to count changesets
- add exc function to simplify exception handling
- combine checksize and checkversion to checklog
- unify missing revlog detection in checklog
- add checkentry to consolidate
- linkrev lookup
- detailed check of linkrev
- detailed check of parents
- duplicate checking
- use checkentry for changelog, manifest, and files
- simplify havecl and havemf
- track all changesets refering to a manifest
- move unnamed file check somewhere more useful
- reorder crosschecks
- fix filenodes crosscheck and add exception handling
- check unpacked size field
- add linkrev and file arguments to err
- track lowest reported linkrev in err
- find linkrev in a couple cases
- sort linkrevs when reporting a bunch of errors against a file
- tidy up lots of messages
- make more robust against damaged indexes
- report first bad changeset if an error is encountered
