fix pool and conv3d unittest when paddle is not build with gpu

Split byref op

Remove redundent pserver block

Correctly implement destructor of ParallelExecutor

Fix FetchTensor on CPU

Add 4 docs to fluid/dev

Clean MultiDevicesGraphBuilder

Remove `dense_vector` from v2 api documents

Use mutex to stablize ncclCtxMap

Add neural transformer leanring rate decay function

Fix bugs in local_scopes

* Add topk Python API.

* Add unit test.

* Remove the repeated API.

Disabling Channel Test to fix CI

Add parallel executor tests

fuse batch norm for conv operator 

- Added Epsilon (preventing softmax output from being too small) for softmax MKLDNN op

Fix conv_mkldnn_op.cc which is causing CI failure

* Fix cpplint warnings in beam_search_decode_op

* Fix cpplint warnings in beam_search_op

* Fix test

* fix

* Fix conv_op.h

* Fix conv_mkldnn_op

* Fix cpplint issues in detection_map_op

Add dist unitest data compare, ensure that dist train have same behavior as local training

Regenerate initializer.rst and add MSRAInitializer to initializer.__all__

- EPS added to softmax mkldnn primitive outcome is limited to training
phase

Fixes after review

clang format fixes

clang format fixes

Mpi enabled