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. 
For this example, it seems better to use List comprehension:
```fsharp
[ for i in 0..p.Length - 1 -> p.[0..i] ]
```

You can create a let binding to avoid `fun p` if you like.