Teach bdiff to support buffer objects manifest.add gives revlog.addrevision a buffer object, which may be cached and used for a second call in the same session (as mq does when pushing multiple patches). The other option would be to cast the buffer to str when caching it.

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