* polish some lost error msg

* add some math file to white list

* polish detail based reviewer commnet

test=develop

test=develop

test=develop

test=develop

* exhaustive search for cuDNN conv.
* Refine code and add unit testing.
* Fix model load in fluid/inference and unit testing in conv2d
* Follow comments.
* Fix compiling test=develop

Fix code to support cpplint syntax check

test=develop

This reverts commit ce7d9b07.

* exhaustive search for cuDNN conv.
* Refine code and add unit testing.
* Clean code
* Fix model load in fluid/inference and unit testing in conv2d
* Follow comments.

fix a few other things

Add an interface to set the number of threads for math function, and set the default value to 1 for inference.

* Add USE_OP of all operators and kernels and remove ARCHIVE_START/END in CMakeLists.txt of inference unittests.

* Remove ARCHIVE_START/END when linking inference shared library.

* Disable some fluid related cmake operations for cross-compiling.

* Add profiling information for inference example, recognize digits.

* Refine the profiling method.

* Correct the use of RecordEvent and simplify recognize_digits.

* Refine load

* Address review comments: round 1

* Make API consistent with python-save/load

* Add another unit test

* Remove commented function

* Fix GPU bug

* Address review comments

* Modify wrt PR 8147

* Fix filenames for combined case

* Fix typo

* Address review comments: round 2

* Unify TestInference by keeping default param in template

* Address review comment

* Fix spacing

Add a new type `Reader` for `VarDesc`, which can holds more than one
LoDTensor.