Avoid circular reference by weak referencing kid's parent

Example:

 Memory : 483876 (kb) with 27181 Nodes 2256 Iq 2248 Message leading to 147285 dicts.

![back dot](https://cloud.githubusercontent.com/assets/2277387/3939388/61f6a7ac-24c6-11e4-92d1-c6f7b9cdec03.png)


Weak ref the parent seems to fix this issue.