Change args to http_FilterReq() to lower level.

After the purge, you will end up in vcl_purge{} from where it will
(at some future date) be possible to order a fresh fetch of the
object.

Doing purge from vcl_recv{} solves half of the object existence
problems in vcl_lookup{}.

	return (error(status_code [ , response_string ]));

next method we'll end up in.

Fixes #1281

We may want a better way to return synthetic objects from
vcl_backend_reponse{}, it looks a bit clumsy in the vtc's so far.

fix the bug (category: "How did _that_ ever work") this uncovered.

and does nothing to make the tests objective any clearer.

difference in any way.

from req.

production of the hash-key.

Fixes	#1296

encapsulated in the vrt_ctx.

with vrt_ctx arguments.

This actually makes some of the macro-expansions in cache_vrt_var.c
simpler and saner...

even newer vrt_ctx argument.