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
<h3 class="changelog">
<a class="title" href="{url|urlescape}rev/{node|short}{sessionvars%urlparameter}">
{desc|strip|firstline|escape|nonempty}
{alltags}
</a>
</h3>
<ul class="changelog-entry">
<li class="age">{date|rfc822date}</li>
<li>by <span class="name">{author|obfuscate}</span> <span class="revdate">[{date|rfc822date}] rev {rev}</span></li>
<li class="description">{desc|strip|escape|websub|addbreaks|nonempty}</li>
</ul>