Also remove operator bool in Error. The Error should be removed
later because it is not necessary for Paddle. We are now using Enforce
to handle error.

1. v2.layer.parse_network does not correctly handle the generation output.
2. GatherAgentLayer does not correctly handle generation output when batch_size > 1
3. Fix CustomStackTrace for rnn group

* Also make ErrorF as a global method.

* Check all files by pre commit hooks

* Use C++ 11 atomic_flag in MacOS as spin lock
* Add unittest for it.

ISSUE=4586495

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1408 1ad973e4-5ce8-4261-8a94-b56d1f490c56