phabricator: fallback to reading metadata from diff for phabread
Differential Revision: https://phab.mercurial-scm.org/D6301
<item>
<title>{tag|escape}</title>
<link>{urlbase}{url|urlescape}rev/{node|short}</link>
<description><![CDATA[{tag|strip|escape|addbreaks}]]></description>
<pubDate>{date|rfc822date}</pubDate>
</item>