This implements the nodesbetween method, and it removes the newer method
and replaces it with calls to nodesbetween.
nodesbetween calculates all the changesets needed to have a complete
revision graph between a given set of base nodes and a given set of
head nodes.
<item>
<title>#desc|firstline|escape#</title>
<link>#url#?cmd=file;file=#file#;filenode=#filenode#</link>
<description><![CDATA[#desc|escape|addbreaks#]]></description>
<author>#author|obfuscate#</author>
<pubDate>#date|rfc822date#</pubDate>>
</item>