TensorFlow: fix some last python3 compatibility issues for 0.6.0.

Change-Id: I3cd6c6e3f3c7755343213e4697c97a09f79fb947

Author: Vijay Vasudevan

tensorflow/models/image/imagenet/BUILD

@@ -10,6 +10,7 @@ py_binary(
     srcs = [
         "classify_image.py",
     ],
+    srcs_version = "PY2AND3",
     visibility = ["//tensorflow:__subpackages__"],
     deps = [
         "//tensorflow:tensorflow_py",

tensorflow/python/ops/gradients.py

@@ -444,7 +444,7 @@ def gradients(ys,
                 op_wrapper = control_flow_ops.MakeWrapper(op)
               in_grads = _AsList(grad_fn(op_wrapper, *out_grads))
               _VerifyGeneratedGradients(in_grads, op)
-              if gate_gradients and len(filter(None, in_grads)) > 1:
+              if gate_gradients and len(tuple(filter(None, in_grads))) > 1:
                 in_grads = control_flow_ops.tuple(in_grads)
           logging.vlog(1, "Gradient for '" + op.name + "'")
           logging.vlog(1, "  in  --> %s",