Small UI fix on homepage

Added `clearfix` class to Post a bounty box.

Before : 
![bountysource](https://f.cloud.github.com/assets/3893573/2453059/7614333e-aed9-11e3-9d4a-e9a1002615cd.png)
After : 
![bountysourcesolution](https://f.cloud.github.com/assets/3893573/2453061/7aa29daa-aed9-11e3-9943-d30bb9a8b6f0.png)