filterfiles: Search as long as the target is a prefix of current. filterfiles was failing to find files for directory arguments if another file existed that started with the directory name and sorted earlier. For example, a manifest of ('foo.h', 'foo/foo') would cause filterfiles('foo') to return nothing. This resolves issue #294.

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