hgweb: fix handling of path for old style template - path from old style are prefixed by '/', make cleanpath strip them - make manifest() use relative paths, that was the only function using '/' prefixed paths

<item>
    <title>#tag|escape#</title>
    <link>{urlbase}{url}rev/{node|short}</link>
    <description><![CDATA[#tag|strip|escape|addbreaks#]]></description>
    <pubDate>#date|rfc822date#</pubDate>
</item>