Fix layout on the registration page for mobile

# BEFORE

![2013-08-13 13 05 51](https://f.cloud.github.com/assets/1108789/954076/9dc52c96-040a-11e3-9d77-5623f3cb3c78.png)

# AFTER

![screenshot_2013-08-14-13-54-43 1](https://f.cloud.github.com/assets/1108789/961536/82c26e58-04d8-11e3-8160-348848ce67d2.png)