Only add scrollbars to <pre> elements if there's too much content to display

These scrollbars make me sad:

![screen shot 2013-09-29 at 1 38 25 pm](https://f.cloud.github.com/assets/1447206/1233712/cbfabd20-293e-11e3-854a-8f8b7f7c3021.png)

I'm going to try to figure out why the code indentation isn't working too..