Add note to 1.0 porting guide about removal of dictionary access to HTTP request objects

HTTP request/response objects

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Dictionary access to ``HttpRequest``

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``HttpRequest`` objects no longer directly support dictionary-style

access; previously, both ``GET`` and ``POST`` data were directly

available on the ``HttpRequest`` object (e.g., you could check for a

piece of form data by using ``if 'some_form_key' in request`` or by

reading ``request['some_form_key']``. This is no longer supported; if

you need access to the combined ``GET`` and ``POST`` data, use

``request.REQUEST`` instead.

It is strongly suggested, however, that you always explicitly look in

the appropriate dictionary for the type of request you expect to

receive (``request.GET`` or ``request.POST``); relying on the combined

``request.REQUEST`` dictionary can mask the origin of incoming data.

Accessing ``HTTPResponse`` headers

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~