Fixed #17504 -- Fixed normalization of email addresses that have '@' in the...

Fixed #17504 -- Fixed normalization of email addresses that have '@' in the name when calling `User.objects.create_user`. Thanks, marw85.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17482 bcc190cf-cafb-0310-a4f2-bffc1f526a37