Bootstrap Cython compilation; Support greenified sendmsg.

`Bootstrap Cython compilation` 的原因是 `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