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

adding a
adding b/a
a
b/a
644 a
644 b/a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 b/a
a
a
b/a
a
b/a
% should fail
abort: unknown revision '2'!
abort: please specify just one revision
a
b/a