Add clear fix to article contain to prevent leakage.

This prevents elements that our floated at the bottom of articles leaking into our sections.

## Before
![Before](http://cl.ly/image/0S2s3E1W143j/Image%202013.08.22%2011%3A35%3A40.png)

## After
![After](http://cl.ly/image/3k0N280p1v0g/Image%202013.08.22%2011%3A39%3A06.png)