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
% should fail
abort: path contains illegal component: .hg/00changelog.i
adding a/a
% should fail
abort: path 'b/b' traverses symbolic link 'b'
% should succeed
% should still fail - maybe
abort: path 'b/b' traverses symbolic link 'b'