[etwist] fix handling of multiple files per field
html5 permits multiple files uploads, which can be expressed as::
<input type='file' multiple='multiple' />
This changeset avoids previous crash. Nothing is changed when a single file is
uploaded (backward compat is thus preserved). When multiple files are uploaded
for a single html input tag, the corresponding web request form key receives a
list of tuples like [('filename-1', IStream1), ('filename-2', IStream2), ...].
closes #2847207.
<html>
<head>
<!-- dependencies -->
<script type="text/javascript" src="../../data/jquery.js"></script>
<script src="../../data/cubicweb.python.js" type="text/javascript"></script>
<script src="../../data/cubicweb.js" type="text/javascript"></script>
<script src="../../data/cubicweb.compat.js" type="text/javascript"></script>
<script src="../../data/cubicweb.htmlhelpers.js" type="text/javascript"></script>
<!-- qunit files -->
<script type="text/javascript" src="../../../devtools/data/qunit.js"></script>
<link rel="stylesheet" type="text/css" media="all" href="../../../devtools/data/qunit.css" />
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<script src="cwmock.js" type="text/javascript"></script>
<script src="test_htmlhelpers.js" type="text/javascript"></script>
</head>
<body>
<div id="main"> </div>
<h1 id="qunit-header">cubicweb.htmlhelpers.js functions tests</h1>
<h2 id="qunit-banner"></h2>
<ol id="qunit-tests">
</body>
</html>