Fixed #7722 - added support for CC in EmailMessage.

Thanks to roberto.digirolamo for the report and initial patch, and
dougvanhorn and SmileyChris for further work on the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14000 bcc190cf-cafb-0310-a4f2-bffc1f526a37