Users with usernames containing uppercase letters cannot log in.

[jtakayama]

User accounts can be created that contain uppercase letters in their usernames, but these accounts cannot log in after they have been created.

To reproduce this step:

1. Log into a Makahiki instance as a user with administrator privileges.
2. Go to http://:8000/challenge_setting_admin/auth/user/add/
3. Set the Username as ALLCAPS. Use any password.
4. Save the new user.
5. Log out.
6. Try to log in as user ALLCAPS. You will see the error "Incorrect username and/or password."