util.system: Use subprocess instead of os.system
subprocess allows the environment and working directory to be specified
directly, so the hacks for making temporary changes while forking is no longer
necessary.
This also fixes failures on solaris where the temporary changes can't be undone
because there is no unsetenv.
{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}