Description:
------------
After calling registerPHPFunctions() and including the php namespace on an XSL stylesheet, I can call global functions (eg date()), but not static class functions (ie testClass::testMethod()).

Reproduce code:
---------------
class testClass {
	function testMethod() {
		return 'testValue';
	}
}
$xslt = new XSLTProcessor;
$xslt->registerPHPFunctions();
$xmlDoc = DOMDocument::loadXML('<root />');

$xslDoc = DOMDocument::loadXML(' 
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl">
	<xsl:template match="/">
		<div><xsl:value-of select="php:function(\'testClass::testMethod\')" /></div>
	</xsl:template>
</xsl:stylesheet>');

$xslt->importStylesheet($xslDoc);
echo $xslt->transformToXML($xmlDoc);

Expected result:
----------------
<div>testValue</div>

Actual result:
--------------
Warning: XSLTProcessor::transformToXml() [function.transformToXml]: Unable to call handler testClass::testMethod() in /home/rob/Projects/sandbox/index.php on line 19

Warning: XSLTProcessor::transformToXml() [function.transformToXml]: xmlXPathCompiledEval: evaluation failed in /home/rob/Projects/sandbox/index.php on line 19

Warning: XSLTProcessor::transformToXml() [function.transformToXml]: runtime error: file /home/rob/Projects/sandbox/ line 4 element value-of in /home/rob/Projects/sandbox/index.php on line 19

Warning: XSLTProcessor::transformToXml() [function.transformToXml]: xsltValueOf: text copy failed in /home/rob/Projects/sandbox/index.php on line 19