Autolink URLs in story description

![image](https://f.cloud.github.com/assets/34378/2306386/09740cba-a284-11e3-85c0-eb26121dca5f.png)
![image](https://f.cloud.github.com/assets/34378/2306391/270ee826-a284-11e3-8785-87b6649d4c75.png)

I'm having a similar problem here to the one I mentioned in #219: `spec/features/stories_spec.rb:153` succeeds when run by itself, but fails otherwise.