hgweb: call process_dates() via DOM event listener
All the hgweb templates include mercurial.js in their header. All
the hgweb templates have the same <script> boilerplate to run
process_dates(). This patch factors that function call into
mercurial.js as part of a DOMContentLoaded event listener.
<div class="page_footer">
<div class="page_footer_text">{repo|escape}</div>
<div class="rss_logo">
<a href="{url|urlescape}rss-log">RSS</a>
<a href="{url|urlescape}atom-log">Atom</a>
</div>
<br />
{motd}
</div>
</body>
</html>