Fixed #12571 -- Attached originating WSGIRequest to test client responses.

Originating WSGIRequests are now attached to the ``wsgi_request`` attribute of
the ``HttpResponse`` returned by the testing client.

Thanks rvdrijst for the suggestion.

docs/topics/testing/tools.txt

@@ -427,6 +427,13 @@ Specifically, a ``Response`` object has the following attributes:
 
         The request data that stimulated the response.
 
+    .. attribute:: wsgi_request
+
+        .. versionadded:: 1.7
+
+        The ``WSGIRequest`` instance generated by the test handler that
+        generated the response.
+
     .. attribute:: status_code
 
         The HTTP status of the response, as an integer. See