message: Improved CTC error message.
diff: @@ -315,7 +315,8 @@ Status CTCLossCalculator::PopulateLPrimes(
  "Saw a non-null label (index >= num_classes - 1) "
  "following a ",
  "null label, batch: ", b, " num_classes: ", num_classes,
  - " labels: ", str_util::Join(l, ","));
  + " labels: ", str_util::Join(label, ","),
  + " labels seen so far: ", str_util::Join(l, ","));
  }
  l.push_back(label[i]);
  }
  