[MINOR] report in the proxies the requirements for ACLs

[MINOR] report in the proxies the requirements for ACLs

This patch propagates the ACL conditions' "requires" bitfield
to the proxies. This makes it possible to know exactly what a
proxy might have to support for any request, which helps knowing
whether we have to allocate some space for certain types of
structures or not (eg: the hdr_idx struct).

The concept might be extended to a lot more types of information,
such as detecting whether we need to allocate some space for some
request ACLs which need a result in the response, etc...