Fixed #6139 -- When sending email, made sure that the "to" and "bcc" sequences...

Fixed #6139 -- When sending email, made sure that the "to" and "bcc" sequences have the same type before concatenating.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6953 bcc190cf-cafb-0310-a4f2-bffc1f526a37