* docs/manual/new_features_2_2.xml: Take a pass at blurbs for auth and cache

    <dl>

      <dt>Authn/Authz</dt>

      <dd>...</dd>

      <dd>The bundled authentication and authorization modules have

          been refactored.  There is a new authentication backend provider

          scheme which greatly eases the construction of new authentication

          backends.</dd>

      <dt>Caching</dt>

      <dd>...</dd>

      <dd><module>mod_cache</module>, <module>mod_disk_cache</module>, and

          <module>mod_mem_cache</module> have undergone a lot of changes

          are now considered production-quality. <a

          href="programs/htcacheclean.html">htcacheclean</a> has been

          introduced to cleanup <module>mod_disk_cache</module> setups.</dd>

      <dt>Proxying</dt>

      <dd>The new <module>mod_proxy_balancer</module> module provides