hgweb: partially revert 4ec58b157265 The change from self.repo.ui.diffopts() to ui.diffopts() causes a traceback when the diff of a changeset should be displayed in the web interface. Revert to self.repo.ui.diffopts() for now.

<item>
    <title>#tag|escape#</title>
    <link>#url#?cs=#node|short#</link>
    <description><![CDATA[#tag|strip|escape|addbreaks#]]></description>
    <pubDate>#date|rfc822date#</pubDate>
</item>