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.

#header#
    <title>#repo|escape# Changelog</title>
    <description>#repo|escape# Changelog</description>
    #entries%changelogentry#
  </channel>
</rss>