[PATCH] public upstream connect and finalize request

[RekGRpth]

>"Try to make it clear why the suggested change is needed,
>and provide a use case, if possible."

It is needed for an upstream plugin, which has its own read and write
infrastructure. (And, of cause, I forgotten publicate
ngx_http_upstream_next)

>Thanks for the details. The suggested changes do not look in line with how upstream >module works: it manages connections itself, and provides protocol-specific callbacks and >filters to make it possible to implement various protocols. You may want to reconsider how >your module works and change it to work with existing upstream interfaces instead.

Unfortunately, I can not modify used third-party library (such as
libpq) and then I need copy some private functions from
ngx_http_upstream.c https://github.com/RekGRpth/ngx_pq_module