setup: try a non-pure version of the local Mercurial if the pure fails
Things like `zstd` can make the pure version fails.
{header}
<title>Mercurial repository not found</title>
</head>
<body>
<div class="page_header">
<a href="{logourl}" title="Mercurial" style="float: right;">Mercurial</a> Not found: {repo|escape}
</div>
<div class="page_body">
The specified repository "{repo|escape}" is unknown, sorry.
<br/>
<br/>
Please go back to the <a href="{url|urlescape}">main repository list page</a>.
</div>
{footer}