message: richen error messages
diff: @@ -198,7 +198,8 @@ Status RecordReader::ReadRecord(uint64* offset, tstring* record) {
  if (!s.ok()) {
  last_read_failed_ = true;
  if (errors::IsOutOfRange(s)) {
  - s = errors::DataLoss("truncated record at ", *offset);
  + s = errors::DataLoss("truncated record at ", *offset,
  + "' failed with ", s.error_message());
  }
  return s;
  }
  @@ -228,7 +229,8 @@ Status RecordReader::SkipRecords(uint64* offset, int num_to_skip,
  if (!s.ok()) {
  last_read_failed_ = true;
  if (errors::IsOutOfRange(s)) {
  - s = errors::DataLoss("truncated record at ", *offset);
  + s = errors::DataLoss("truncated record at ", *offset,
  + "' failed with ", s.error_message());
  }
  return s;
  }
  