Description:
------------
When calling a PHP function from XSL I get a failure 
message (see below). 

Reproduce code:
---------------
<?php
$xml = '<root></root>';

$xsl = <<<EOT
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
   <foobar>
    <xsl:value-of select="php:function('date', 'r')" />
   </foobar>
  </xsl:template>
</xsl:stylesheet>
EOT;

$xslt = new xsltProcessor();
$xslt->registerPHPFunctions();

$xslt->importStyleSheet(DomDocument::loadXML($xsl));
print $xslt->transformToXML(DomDocument::loadXML($xml));
?>

Expected result:
----------------
<foobar>Current date</foobar> 

Actual result:
--------------
Warning: xmlXPathCompOpEval: function function bound to 
undefined prefix php 
in /home/hans/tests/php5/xsl/convert.php on line 18 
 
Warning: xmlXPathCompiledEval: 1 object left on the stack 
in /home/hans/tests/php5/xsl/convert.php on line 18 
<?xml version="1.0"?> 
<foobar>r</foobar>