work around python bug on solaris 10.
write to file opened mode 'a+' should write to end of file and update
offset pointer, but does not (solaris 10 has python 2.3.3).
fix is to always seek.
#header#
<title>Mercurial repositories index</title>
</head>
<body>
<h2>Mercurial Repositories</h2>
<table>
<tr>
<td>Name</td>
<td>Description</td>
<td>Contact</td>
<td>Last change</td>
<td> </td>
<tr>
#entries%indexentry#
</table>
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