verify: report first bad changeset
- 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
abort: Failed to parse .../t/.hg/hgrc
File contains no section headers.
file: .../t/.hg/hgrc, line: 1
'invalid\n'