MEDIUM: http: unify acl and sample fetch functions

MEDIUM: http: unify acl and sample fetch functions

The following sample fetch functions were only usable by ACLs but are now
usable by sample fetches too :

    cook, cook_cnt, cook_val, hdr_cnt, hdr_ip, hdr_val, http_auth,
    http_auth_group, http_first_req, method, req_proto_http, req_ver,
    resp_ver, scook, scook_cnt, scook_val, shdr, shdr_cnt, shdr_ip,
    shdr_val, status, urlp, urlp_val,

Most of them won't bring much benefit at the moment, or are even aliases of
existing ones, however they'll be needed for ACL->SMP convergence.

A new val_usr() function was added to resolve userlist names into pointers.

The http_auth_group ACL forgot to make its first argument mandatory, so
there was a check in cfgparse to report a vague error. Now that args are
correctly parsed, let's report something more precise.

All urlp* ACLs now support an optional 3rd argument like their sample
counter-part which is the optional delimiter.

The fetch functions have been renamed "smp_fetch_*".

Some args controls on the sample keywords have been relaxed so that we
can soon use them for ACLs :

  - cookie now accepts to have an optional name ; it will return the
    first matching cookie if the name is not set ;
  - same for set-cookie and hdr