make auto-registry layers supporting specified output

python/paddle/v2/fluid/registry.py

 #  Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
 #
-#Licensed under the Apache License, Version 2.0 (the "License");
-#you may not use this file except in compliance with the License.
-#You may obtain a copy of the License at
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
 #
 #    http://www.apache.org/licenses/LICENSE-2.0
 #
-#Unless required by applicable law or agreed to in writing, software
-#distributed under the License is distributed on an "AS IS" BASIS,
-#WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-#See the License for the specific language governing permissions and
-#limitations under the License.
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
 import re
 import cStringIO
 import warnings
@@ -167,13 +167,18 @@ def register_layer(op_type):
             inputs[ipt.name] = val
 
         outputs = dict()
-        out = helper.create_tmp_variable(dtype=dtype)
-        outputs[o_name] = [out]
+        out = kwargs.pop(_convert_(o_name), [])
+        if out:
+            out_var = out[0] if (isinstance(out, list) or
+                                 isinstance(out, tuple)) else out
+        else:
+            out_var = helper.create_tmp_variable(dtype=dtype)
+        outputs[o_name] = [out_var]
         for name in intermediate_output_names:
             outputs[name] = [helper.create_tmp_variable(dtype=dtype)]
         helper.append_op(
             type=op_type, inputs=inputs, outputs=outputs, attrs=kwargs)
-        return helper.append_activation(out)
+        return helper.append_activation(out_var)
 
     func.__name__ = op_type
     func.__doc__ = _generate_doc_string_(op_proto)