Add flexible width arrow button

Chrome (long): 

![screen shot 2014-06-03 at 12 12 13 pm](https://cloud.githubusercontent.com/assets/206973/3165668/25f49672-eb57-11e3-9c20-bd69b330a450.png)

IE 9 (artifacts are browserstack):

![screen shot 2014-06-03 at 12 31 21 pm](https://cloud.githubusercontent.com/assets/206973/3165679/4bb2cb36-eb57-11e3-98ab-5daf9f7f9d56.png)