Description:
------------
issues a warning when passing an array value as "The element name"

Reproduce code:
---------------
<?php   
    $test = array('foo','bar');
    $testarr = array('foo' => array('1','2','3'),'bar' => array('1','2','3'));    
    $titles = array('item_1', 'item_2');
        
    header('Content-Type: text/xml; charset=iso-8859-1');
    
    $xml = new xmlWriter();
    $xml->openMemory();
    $xml->setindent(true);
    $xml->setindentstring('  ');
    $xml->startDocument('1.0','iso-8859-1');
    $xml->startElement ('root');          
    for($i=0;$i<count($test);$i++) {                     
        $xml->writeElement ('title', $test[$i]);
        $xml->startElement ('data');
        for($j=0;$j<count($testarr[$test[$i]]);$j++) {
            $xml->writeElement ($titles[$j], 'test');    
        }
        $xml->endElement();
    }
                
    $xml->endElement();
    print $xml->outputMemory(true); 
?>

Expected result:
----------------
No warning.

Actual result:
--------------
<b>Warning</b>:  XMLWriter::writeElement() [<a href='function.XMLWriter-writeElement'>function.XMLWriter-writeElement</a>]: Invalid Element Name in <b>D:\devel\bug\index.php</b> on line <b>18</b>

However the xmldata is printed correctley if the source is checked.