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 show unknown
? unknown
removing b
%% Should show unknown and b removed
R b
? unknown
%% Should show a and unknown
a
unknown