*   Allow `DNNBoostedTreeCombinedEstimator` to work with core versions of
        feature columns and losses.
    *   Add non-linear image warping ops: `tf.contrib.image.sparse_image_warp`,
        `tf.contrib.image.dense_image_warp`, and
        `tf.contrib.image.interpolate_spline`.
    *   Fix bug in `tf.contrib.opt.MultitaskOptimizerWrapper` where types of
        tensors were mismatched.
*   Other: