Fixed #5898 -- Changed a few response processing paths to make things harder to get wrong and easier to get right. Previous behaviour wasn't buggy, but it was harder to use than necessary.

We now have automatic HEAD processing always (previously required ConditionalGetMiddleware), middleware benefits from the Location header rewrite, so they can use relative URLs as well, and responses with response codes 1xx, 204 or 304 will always have their content removed, in accordance with the HTTP spec (so it's much harder to indavertently deliver invalid responses).

Based on a patch and diagnosis from regexbot@gmail.com.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6662 bcc190cf-cafb-0310-a4f2-bffc1f526a37