* improve save and load behaviour, test=develop

* code cleaning, test=develop

* disable check_guards and update_guards in release version, test=develop

* fix compilation issue, test=develop

* add buddy_allocator speed test data, test=develop

* fix compilation issue, test=develop

* fix comment, test=develop

* update function names according to the google C++ style guide, test=develop

* tweak the test data format, test=develop

* move buddy_allocator_test_data to paddle/fluid/testdata, test=develop

* add accessor and mutator for Desc, test=develop

* add retry_allocator for gpu, test=develop

* follow chengduoZH's comments, test=develop

* follow huihuang's comments,test=develop

* change f,l in enforce.h to be file,line, test=develop

* increase code coverage by adding unittests, test=develop

* fix CMakeLists.txt, test=develop

GPU allocation uses fraction of available memory, also fix the GetUsed without lock

modify allocator strategy
remove changes of legacy buddy_allocator
test=develop

test=develop

test=develop

Fix code to support cpplint syntax check

test=develop

By shell command

```bash
sed -i 's#ifdef PADDLE_ONLY_CPU#ifndef PADDLE_WITH_GPU#g' `find ./paddle/ -name '*.h' -o -name '*.cc' -o -name '*.cpp' -o -name '*.c' -o -name '*.cu'`
sed -i 's#ifndef PADDLE_ONLY_CPU#ifdef PADDLE_WITH_GPU#g' `find ./paddle/ -name '*.h' -o -name '*.cc' -o -name '*.cpp' -o -name '*.c' -o -name '*.cu'`
```

* Free will be added soon