“b85af464de88af8af7e01e1b130fdc32d1436e56”上不存在“test/legacy_test/test_dist_fleet_ps2.py”
* Fix bug in MergeModel.cpp. * Add a c-api inferface to initilize the thread environment of Paddle and add a GPU example. * Add some note for paddle_init_thread and move the inplementation of paddle_error_string into a .cpp file. * Add some comments.