SourceCodeClassifier marks unused open declarations

![image](https://cloud.githubusercontent.com/assets/873919/3530402/235c77fe-07a4-11e4-92f4-95802ae5e057.png)

I will add tests but it basically works. 
Can you add comments on `qualifiedSymbols` and `symbolUsesWithoutNested`? The code below looks quite hairy.