windows: fix use of undefined exception (issue1707)
This fixes the implied reliance on pywin32 and the win32 module. This
also fixes a regression in ae275ad46bd0 that made Mercurial unusable
without pywin32.
{header}
<title>Mercurial repository not found</title>
</head>
<body>
<div class="page_header">
<a href="http://mercurial.selenic.com/" 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}">main repository list page</a>.
</div>
{footer}