[1.2.X] Fixed #13687 -- Corrected request/response docs that mistakenly...

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

Backport of r13529 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13535 bcc190cf-cafb-0310-a4f2-bffc1f526a37