mod_proxy: Ignore (and warn about) enablereuse=on for ProxyPassMatch when

mod_proxy: Ignore (and warn about) enablereuse=on for ProxyPassMatch when
           some dollar substitution (backreference) happens in the hostname
           or port part of the URL.

Address or connection reuse can't work when the autority part of the URL is
dynamic (single origin server[:port] handled/assumed in the reslist). Detect
such cases and unset worker->s->is_address_reusable to disable reuse regardless
of enablereuse/disablereuse.

* modules/proxy/proxy_util.c(ap_proxy_define_worker_ex):
  Lookup for $n substitution in the hostname[:port] when parsing the URL and
  if present, set worker->->is_address_reusable=0 / worker->s->disablereuse=1.

* modules/proxy/proxy_util.c(ap_proxy_initialize_worker):
  Don't overwrite worker->s->is_address_reusable from enablereuse/disablereuse
  parameters, and set both consistently.

* docs/manual/mod/mod_proxy.xml:
  Add ProxyPassMatch compatibility note about key=value parameters handled with
  $n substitutions since 2.4.47.
  Document the specificities of enablereuse/disablereuse w.r.t. $n subsitutions
  in the different part of the URL.
  Axe the note about unparsable URLs when the $n substitution happens in the
  port, this has been addressed in 2.4.47 too (and works now).

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1904513 13f79535-47bb-0310-9956-ffa450edef68