Backport to v2.4:

Backport to v2.4:

  *) mod_proxy: Allow to set a TTL for how long DNS resolutions to backend
     systems are cached.
     In order to solve merge conflicts this proposal also backports:

     mod_proxy: Add optional third argument for ProxyRemote, which
     configures Basic authentication credentials to pass to the remote
     proxy.  PR 37355. (r1881790)

     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. (r1904513)

     Trunk version of patch:
        https://svn.apache.org/r1881790
        https://svn.apache.org/r1904513
        https://svn.apache.org/r1909400
        https://svn.apache.org/r1909401
        https://svn.apache.org/r1909402
        https://svn.apache.org/r1909451
        https://svn.apache.org/r1912459
        https://svn.apache.org/r1913432
        https://svn.apache.org/r1913534
     Backport version for 2.4.x of patch:
       https://patch-diff.githubusercontent.com/raw/apache/httpd/pull/390.diff
     Can be applied via apply_backport_pr.sh 390
     +1: rpluem, ylavic, minfrin

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1913907 13f79535-47bb-0310-9956-ffa450edef68