relnotes: enable extension when running releasenotes command
Last night, when I was working on different machine, the test worked, now on a
different machine it does not. Looks like we should make sure releasenotes
extension is loaded.
Differential Revision: https://phab.mercurial-scm.org/D4425
{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>