objcore/req symmetry and Obj->methods

[Dridi Boukelmoune]

> We have people asking for the "send the request to N backends and
> use the first response you get" functionality - which is the exact
> same problem as obj.body streaming is, so for req.body there is
> a plain use-case.

Couldn't this functionality be implemented in a VMOD instead?

A director could spawn multiple backend requests and pick the first
one, but either way, we'd need a way to pin several sub-transactions
to a bereq transaction.

Dridi