* Add distributed implementation for recommender system

* Addressing code review feedback

fix openblas build

* remove pick dependency

* fix bug

* small fix

* modify executor.py for save and load

* clean code

* Add usage example

* refine executor run function

* fix bug

* refine executor code

* fix block bug

* fix comments

* fix bug

* fix pass num

Fix get_inference_program

fix a bug

* aysnc send/recv, seriliaze/deserialize using threadpool

* implement paralell deserialization correctly

Add `ProgramDesc` storage

Rename is_compile_gpu to is_compiled_with_cuda

 Make get_inference_program support for Evaluator.

Add the wrapper for multi-head scaled dot product attention.

Disable the unstable unittest

Test parallel do with multiple input

The English of the previous API is bad.

Deepcopy ParamAttr while creating parameter.

Refine profiler and expose to Python.

Fix LoD calculate of im2seq

Add pyton wrapper for row conv operator.

Conflicts:
	python/paddle/v2/fluid/layers/nn.py
	python/paddle/v2/fluid/tests/test_layers.py

Make Parallel.Do support sparse gradients 

Use ExternalProject_Add to download and install boost.

Fix warnings in priorbox, sequence_reshape and ctc_align_op

Enhance image.py for gray image.