Rename cache_response.c to cache_http1_deliver.c and make it responsible
for all deliveries, streaming or non-streaming
New VTLA:  V1D - HTTP1 delivery
Also rename the function calls.
Move code around
minor polish
Add yet a VTLA: "VDP" Delivery processors

These are stackable, and does stuff on the way out.

The bottom one points to HTTP/1 ie. WRW for now.

On top of that we can push Range: processing.

Modularizing this, makes it trivial to enable Range: support for
delivery-side gunzip.

(Committed above the Elbe)
Turn delivery-side gunzip into a VDP
Polish
Make the VDP ptr argument const
Polish
Fix buglet
Fix a fine point in this test-case:  We can get a Content-Length on
a 304 response, but we still don't get the body.
Fix other 304 return cases to not expect a body
IMS decision is protocol-independent
Single test for Range-qualifying request
Move the stream-stopper all the way to where streaming will happen
Atomically grab the busyobj, if there is one.
Stream.

(Don't tell me nothing good ever comes from DB's delayed trains...)
Add a missing #include
Update our copy of ZLIB to 1.2.8