* compile with nccl2

* add ncclGroup; it is necessary in nccl2

* add back libnccl-dev

* Refine Type system

* Fixing type inference

* Fixed create_reader_op.cc

* Fix var_desc.h

* Fixed executor.cc

* Fix shape_inference.h

* Fixed create_reader_op.cc

* Fix tensor_util.h

* Fixed var_type_inference_test.cc

* Fix shape_inference.cc

* Fixed sum_op.c

* Fixed read_op.cc

* Fix var_type.h

* Fixed beam_search_decode_op.cc

* sendrecvop_utils.cc

* Fix operator.cc

* Fixed lookup_table_op.cc

* Fixed op_desc.cc

* Fixed get_places_op.cc

* Fixed lod_rank_table_op.cc

* Fixed beam_search_op.cc

* Fix var_desc.cc

* Fixed lod_tensor_to_array_op.cc

* Fixed while_op.cc

* Fix program_desc_test.cc

* tensor_array_read_write_op.cc

* Fix assign_op.cc

* Fix executor.cc

* Fix protobuf.cc

* Fix protobuf.cc

And some minor fixes on comments.

* move float16 into fluid

* fix include

* move to platform folder

* "merge random generator kernel and mul"

* "fix dropout"

* Implement multibox loss wrapper in Python API.

* Add some wrappers for SSD detection.

* Fix conflicts.

* Add unit testing for SSD loss wrapper.

* Update doc in Python API.

* Refine unit testing.

* Add more unit testing and update some interface arguments.

* refine inference_lib_dist after code move, and add it to docker/build.sh

* remove is_directory in inference_lib.cmake

* Add softmax_with_cross_entropy and smooth_l1 in Python API.

* Fix doc format.

* dynamic send/recv selected rows

* update by comment

* fix by comment

Fix #8368

* Fix constructor bug in mixed_vector

* Fix warnings

* Clean code

* Extract for-loop init. Make nvcc happy

* dist train support lr decay

* update by comment

* revert elementwise method creator

* delete comment