Fix tooltip arrow

Give the arrow a border and let file paths live on a single line.

Before:
![tooltip-before](https://cloud.githubusercontent.com/assets/122102/3680513/5c5b4a6a-12af-11e4-9948-9ba8539ab6e7.png)

After:
![tooltip-after](https://cloud.githubusercontent.com/assets/122102/3680514/5c7b0c92-12af-11e4-9f3a-e245ff1a905b.png)