qiniu/ios-sdk — pull request #40 by yangchenlarkin (2014-04-03 08:00:51+00:00)
Title: repair a retain cycle

我是参考的这两个地方的讨论：
http://stackoverflow.com/questions/19884403/recursive-block-and-retain-cycles-in-arc
http://stackoverflow.com/questions/13090598/recursive-block-retain-cycles