backward incompatibility with regard to your old checkpoints containing such
    RNN cells, in which case you can use the tool
    [checkpoint_convert script](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/contrib/rnn/python/tools/checkpoint_convert.py)
    to convert the variable names in your old checkpoints.
*   Many of the RNN functions and classes that were in the `tf.nn` namespace