Bootstrap Cython compilation; Support greenified sendmsg.

#### Bootstrap Cython compilation

 `pip install git+git://github.com/douban/greenify.git#egg=greenify`会报错，PR后可通过`pip install git+git://github.com/mckelvin/greenify.git@sendmsg#egg=greenify` 测试。

#### Support greenified sendmsg

为libmc支持gevent做准备。


cc @windreamer