*   saved_model is available as `tf.saved_model`.
*   Empty op is now stateful.
*   Improve speed of scatter_update on the cpu for ASSIGN operations.
*   Change `reduce_join` to treat `reduction_indices` in the same way as other
    `reduce_` ops.
*   Move `TensorForestEstimator` to `contrib/tensor_forest`.
*   Enable compiler optimizations by default and allow configuration in
    configure.