phases: track phase movements in 'advanceboundary'
Makes advanceboundary record the phase movement of affected revisions in
tr.changes['phases'].
The tracking is not usable yet because the 'retractboundary' function can also
affect phases.
We'll improve that in the coming changesets.
<item>
<title>{bookmark|escape}</title>
<link>{urlbase}{url|urlescape}rev/{node|short}</link>
<description><![CDATA[{bookmark|strip|escape|addbreaks}]]></description>
<pubDate>{date|rfc822date}</pubDate>
</item>