Fix bug #20631. The max length of the email is 254 

How you can see in the next link the max length of an email is 254 chars. Now we have only 75 chars...

http://stackoverflow.com/questions/386294/what-is-the-maximum-length-of-a-valid-email-address

Pull request related:

https://github.com/django/django/pull/1291

Ticket related:

https://code.djangoproject.com/ticket/20631

With this pull request we can customize the max length of the emails.

The max length does not change directly, because "At present we do not have the ability to make schema changes in core and so we cannot change the underlying database field of any given model field" (Marc Tamlyn, @mjtamlyn)