Don't apply responsive-img to cutouts on mega-full

Before:
![screen shot 2014-10-10 at 15 01 18](https://cloud.githubusercontent.com/assets/1607666/4593413/d1f930d4-5085-11e4-8188-0af933b1c265.png)

After:
![screen shot 2014-10-10 at 15 01 34](https://cloud.githubusercontent.com/assets/1607666/4593412/d1f4416e-5085-11e4-9625-761b54c50ab6.png)