Duplicate username can be registered

What steps will reproduce the problem?
In some way, the user can send the registration request twice at the same time. 

What is the expected output? What do you see instead?
The later request should be rejected. But if the database transaction take a 
longer time, the later request also succeeded.

Please use labels and text to provide additional information.
The jforum_users table scheme is lack of unique constraint on username field. 
We should add one for this.

Original issue reported on code.google.com by andow...@gmail.com on 15 Sep 2012 at 3:47

Attachments:

[duplicate username.png](https://storage.googleapis.com/google-code-attachments/jforum2/issue-41/comment-0/duplicate username.png)

mheinzerling / jforum2

Duplicate username can be registered #41