This comes with a big apology to Geoff Simmons:  I should have
tackled Conditional Fetch before even thinking about streaming
and therefore this has taken much longer than it should.

state engine a bit while here.

Add author information to some files with significant changes.

VCL type, we can simplify the VCC backend code somewhat.

VCL created simple directors.

pass, it will be anyway.

Fixes #1335

The only real trouble was purges, and they now have their own vcl_purge{}

Sorry for the detour...

(Don't tell me nothing good ever comes from DB's delayed trains...)

a 304 response, but we still don't get the body.

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)

for all deliveries, streaming or non-streaming

off stored objects.

We used to need this in struct obj, so we could munge obj.http, but
we don't allow that any more.