Add flexible width arrow button

New (with 10px overlap + right arrow floated right):

IE 9:

![image](https://cloud.githubusercontent.com/assets/206973/3165971/646e606e-eb5b-11e3-8a13-9720b3f9514b.png)

Chrome (long):

![image](https://cloud.githubusercontent.com/assets/206973/3165885/58be03ba-eb5a-11e3-8872-c896fa398d3f.png)