Fixed #14878 -- Clarified the way verbose_name_plural is used in generic list...

Fixed #14878 -- Clarified the way verbose_name_plural is used in generic list views as a context variable. Thanks to diegueus9 for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15133 bcc190cf-cafb-0310-a4f2-bffc1f526a37