This fixes a bug that Chris Mason found. As for a test case, I can't think of one. It's a very weird case. Basically, if there is a file listed as changed in the changelog entry, but not showing up in any of the associated manifest entries, hg would abort when trying to create a changeset. Now it just decides the file must not have any versions relevant to the changeset.

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