Comment 3 for bug 1030031

We weren't, but now we are:

                  if ( scalar @$diffs ) {
                     # "chunk" is the chunk number. See the SELECT
                     # statement in RowChecksum::find_replication_differences()
                     # for the full list of columns.
                     map { $diff_chunks{ $_->{chunk} }++ } @$diffs;
                  }

Then scalar keys %$diff_chunks is the number of distinct chunks that differ on all slaves.