dirstate: stringify a few exception messages
Built in exceptions want str, and ProgrammingError converts bytes to str
internally (because it subclasses RuntimeError).
{header}
<id>{urlbase}{url|urlescape}atom-log/tip/{file|escape}</id>
<link rel="self" href="{urlbase}{url|urlescape}atom-log/tip/{file|urlescape}"/>
<title>{repo|escape}: {file|escape} history</title>
{latestentry%feedupdated}
{entries%changelogentry}
</feed>