Added password strength verification.

Hi,

I've added a minor enhancement where password fields need to have at least 6 chars and contain at least 1 number.

Thanks for the awesome work!
Cassi
![image](https://f.cloud.github.com/assets/598642/721548/18dc0d44-dfe6-11e2-9f13-1b17c3fd2a79.png)