Security notice

• The __str__() method of the SocialToken model returned the access token. As a consequence, logging or printing tokens otherwise would expose the access token. Now, the method no longer returns the token. If you want to log/print tokens, you will now have to explicitly log the token field of the SocialToken instance.
• Enumeration prevention: the behavior on the outside of an actual signup versus a signup where the user already existed was not fully identical, fixed.