[PATCH 3 of 3] Upstream: add support for trailers in HTTP responses

[Piotr Sikora]

Hey Maxim,

> Overral, this patch looks at most half-ready, as it doesn't even
> try to implement sending trailers (r->expect_trailers is never
> set), lacks any support for trailers in the cache, and so on.

Actually, it's pretty much ready... r->expect_trailers is supposed to
be set by upstream modules (i.e. proxy or 3rd-party upstream module),
and not by the upstream module itself.

But I can see how it can be hard to review only part of the feature,
so I'm going to drop this for now (mostly to speed up the turnaround
of code reviews), and I'll send this later, along HTTP/2 patchset that
uses those changes.

Best regards,
Piotr Sikora