* When SWIG_PY is not enabled, paddle.v2 package cannot be used.
* When PYTHON is not enabled, PyDataProvider cannot be used.

Fix issue #1920

* Fix #1877

Currently, Paddle only support Python use the sample version of
Protobuf that CPP do.

* `pip install` using `find` utility

* set PYTHON_HOME outside the paddle processes.

* Pre-allocated buffer for int scanner

* Also test std::vector
* Use std::vector to PadConf

RecurrentLayerGroup for training.

Otherwise, it will create many containers which are not usefull.