Fixed #13687 -- Corrected request/response docs that mistakenly suggested...

Fixed #13687 -- Corrected request/response docs that mistakenly suggested __getitem__ and __delitem__ were case sensitive. Thanks to master for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13529 bcc190cf-cafb-0310-a4f2-bffc1f526a37