allow @ in username
Merge remote-tracking branch 'upstream/master'
if profile instance create in signal for User model, this "create" will fail with IntegrityError
if profile instance create in signal for User model, this "create" will fail with IntegrityError
Error in add extra fields in signup form

The previous code was trying to add the extra fields to the user model
instead of the profile.
Merge pull request #437 from fsouto/master

Documentation: error adding extra fields to user profile
Merge pull request #422 from bsavelev/master

allow @ in url usernames