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 print nothing
# should fail
abort: path 'b/x' is inside repo 'b'
abort: path 'b/x' is inside repo 'b'
# should fail
abort: path 'b/x' is inside repo 'b'
# should arguably print nothing
# should fail
abort: path 'b/a' is inside repo 'b'