fix appendfile problem on macos.
when i open file with mode 'a+' on linux, seek position is 0.
on macos seek position is end of file instead. not documented.
#header#
<title>#repo|escape#: changelog</title>
<link rel="alternate" type="application/rss+xml"
href="?cmd=changelog;style=rss" title="RSS feed for #repo|escape#">
</head>
<body>
<div class="buttons">
<a href="?cmd=tags">tags</a>
<a href="?mf=#manifest|short#;path=/">manifest</a>
<a type="application/rss+xml" href="?style=rss">rss</a>
</div>
<h2>changelog for #repo|escape#</h2>
<form action="#">
<p>
<label for="search1">search:</label>
<input type="hidden" name="cmd" value="changelog">
<input name="rev" id="search1" type="text" size="30">
navigate: <small class="navigate">#changenav%naventry#</small>
</p>
</form>
#entries%changelogentry#
<form action="#">
<p>
<label for="search2">search:</label>
<input type="hidden" name="cmd" value="changelog">
<input name="rev" id="search2" type="text" size="30">
navigate: <small class="navigate">#changenav%naventry#</small>
</p>
</form>
#footer#