Fix a link in the caching guide.

        <dt>Two-state key/value shared object caching</dt>

        <dd>

            <module>mod_socache</module>

            The <a href="socache.html">shared object cache API</a> (socache)

            and its provider modules provide a

            server wide key/value based shared object cache. These modules

            are designed to cache low level data such as SSL sessions and