[1.0.X] Fixed a typo and clarified how django.core.mail.outbox works in the...

[1.0.X] Fixed a typo and clarified how django.core.mail.outbox works in the testing framework. Fixed #9237.

Backport of r9140 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9142 bcc190cf-cafb-0310-a4f2-bffc1f526a37