Added "Claim a username" tab to make Auth/Login/Reg easier. 

Previously, a user had to click "Forgot password?" and then "I have an activation code." Virtually no-one who had reserved a username found that logical.

The goal of this was to make Auth/Login/Reg simpler and more intuitive. I simply created a 'Claim a username' tab out of elements on the page. It basically asks users to submit the "forgot password" form but doesn't call it that and then takes them to the "I have an activation code" tab. I also added a few lines of explanatory text.

All told, it looks like this, and works on my computer.  
![claimausername](https://f.cloud.github.com/assets/521978/765691/48f02674-e837-11e2-8ed4-fef8c0b5af7d.jpg)
![activate](https://f.cloud.github.com/assets/521978/765693/48f39962-e837-11e2-8306-7473d17fed20.jpg)

To make room for the "Claim a username" tab I shortened the "Forgot your password" tab to just "Forgot" so it wouldn't fall on a new line. 
![forgottenpassword](https://f.cloud.github.com/assets/521978/765692/48f42f1c-e837-11e2-9661-f67a86672b69.jpg)