* refine_dropout_mem,test=develop

* # This is a combination of 14 commits.
# The first commit's message is:
remove ut test_dist_word2vec in mac ci, will fix it in private, test=develop (#17066)

# This is the 2nd commit message:

Fleet unify distributed training (#16791)

* implement distributed transpiler with fleet
# This is the 3rd commit message:

ParallelDyGraph with GPU collective mode (#16827)

implement dygraph.parallel.DataParallel to hook reduce op.

# This is the 4th commit message:

Init mixed precision training interface (#16856)

* Init mixed precision training interface

* Add fp16 test script

test=develop

* All initializers support float16

test=develop

* Code cleanup & add more code annotations

test=develop

* Update API spec

test=develop

* Add usage example in doc

test=develop

# This is the 5th commit message:

fix reference_count_pass,test=develop (#17060)

test=develop
# This is the 6th commit message:

Speedup roi_perspective_transform op by caching the information of linear interpolation in forward (#17090)

* Cache the information of linear interpolation in forward and use it in backward.
test=develop

* Fix cuda kernel.
test=develop

# This is the 7th commit message:

remove unnecessary prepare_data (#17080)

test=develop
# This is the 8th commit message:

fix interpolate cu. test=develop (#17101)

# This is the 9th commit message:

test=develop, double backward leaky_relu (#17067)

backward of backward: leaky_relu
# This is the 10th commit message:

fix fuse optimizer ops (#17102)

test=develop
# This is the 11th commit message:

truncated_gaussian_random supported in distributed training, test=develop (#17091)

# This is the 12th commit message:

 Detailed coordinate description for yolov3 loss (#17007)

* Detailed coordinate description for yolov3 loss

test=develop

* modified api.spec

test=develop

* modified loss name

* fix api.spec

test=develop

* polish description

test=develop

* modified api.spec

test=develop

# This is the 13th commit message:

fix test_weight_decay (#17109)

test=develop
# This is the 14th commit message:

Path flag (#17105)

* fix python/paddle/fluid/__init__.py detecting problems

1. Use CudnnWorkspaceHandle in exhaustive search of conv_cudnn.
2. For Ops using CudnnWorkspaceHandle in exhaustive search, release their GPU memory after exhaustive search.

test=develop

* fix python/paddle/fluid/__init__.py detecting problems

test=develop

* Detailed coordinate description for yolov3 loss

test=develop

* modified api.spec

test=develop

* modified loss name

* fix api.spec

test=develop

* polish description

test=develop

* modified api.spec

test=develop

test=develop

backward of backward: leaky_relu

test=develop

Speedup roi_perspective_transform op by caching the information of linear interpolation in forward (#17090)

* Cache the information of linear interpolation in forward and use it in backward.
test=develop

* Fix cuda kernel.
test=develop

test=develop

* Init mixed precision training interface

* Add fp16 test script

test=develop

* All initializers support float16

test=develop

* Code cleanup & add more code annotations

test=develop

* Update API spec

test=develop

* Add usage example in doc

test=develop

implement dygraph.parallel.DataParallel to hook reduce op.

* implement distributed transpiler with fleet

add checkpoint functions for graph. test=develop

* resolve #17057

Fixed the bug that fuse_relu/fuse_residual option couldn't be passed to class TestConv2dInt8Op.

test=develop

* Fix the bug of test_conv2d_int8_mkldnn case which raised by improper parameter passing.

test=develop

fix runtime_context_cache bug when gpu model has an op runs only on cpu

1. specify the cuda arch name and bin to decrease the compile time for inference test=develop
2. simplify the script and add comments
3. remove the fluid process from cicheck

update pip version in Readme to 1.4.1

test=develop

test=develop

update Readme and releasenote for 1.4.1

* Add fuse momenutum ops

fix nccl wrapper on windows

test=develop

* make_conv_cudnn_ws_size_configurable, test=develop

* change std::max to std::min
test=develop

fix potential hung in generate proposals, test=develop

fix split for dimension judgment

update ngraph version

test=develop

test=develop

reduce unittest time by rename testcuda to has_cuda

Support backward of backward for Relu and add a new gradient checker by comparing theoretical and numerical Jacobian. (#16862)

* Support backward of backward and a new gradient checker
* Rename decorators.py to decorator_helper.py, since Python on Windows CI has decorators package.

1. Add ReluDoubleGradMaker when register relu_grad.
2. Add a new gradient checker by comparing theoretical and numerical Jacobian.  Check double gradients by double_grad_check.

fix bug in save, test=develop

* move gc test to op_test
test=develop

* Revert "move gc test to op_test"

This reverts commit cf15da65c38f57c91f53b3d8b3c2365d4aa86016.

* enable gc test in some ops
test=develop