Description:
------------
php:functionString tries to access objects with their names in lowercase. when you use autoloader to include your classes it generates fatal error because it cannot find the proper php file.

Reproduce code:
---------------
<?php //FILE AutoLoaded.php 
class AutoLoaded { public static function printText($text) { return $text; }} 
?>

<?php //FILE index.php
$xsl=<<<EOSTRING
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl" xsl:extension-element-prefixes="php">
<xsl:template match="xml"><xsl:value-of select="php:functionString('AutoLoaded::printText',@dummy)" disable-output-escaping="yes"/>
</xsl:template></xsl:stylesheet>
EOSTRING;
$xml='<xml dummy="everything is ok"/>';
function __autoload($className) {
    echo $className."\n";
    static $classes = array('AutoLoaded'=>'AutoLoaded.php');
    require_once($classes[$className]);
}
$doc = new DOMDocument('1.0','utf-8'); $doc->loadxml($xml); $xslt = new DOMDocument(); $xslt->loadxml($xsl);
$proc = new XSLTProcessor(); $proc->registerPHPFunctions(); $proc->importStyleSheet($xslt);
$proc->transformToXML($doc);
?>

Expected result:
----------------
AutoLoaded

Actual result:
--------------
autoloaded
Fatal error: require_once() [function.require]: Failed opening required ....