bug 3063 - ability to log in with long email addresses

When you use emails for sign in (for example, using the LDAP authentication backend) it might happen that a 30 character limit on the username field prevents certain email addresses from being entered. 

For example see, https://bugzilla.mozilla.org/show_bug.cgi?id=871921

This happens because you have a `<input name="username" maxlength="30" ...>` on the login template.