Description:
------------
Changing the directory before using using simplexml seems to cause a warning. 

The warning is generated from within libxml2 and is WIN32 specific.

libxml2s' xmlInitializeCatalog() function in catalog.c tries to locate a directory of some catalog files, fails due the chdir() performed in PHP.

Reproduce code:
---------------
<?php

		$xml = '..//config.xml';
		$dir = dirname(realpath($xml));
		var_dump($dir);
		var_dump(chdir($dir));
		$doc = simplexml_load_file(basename($xml));
		var_dump(htmlspecialchars($doc->asXML()));
?>

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

Actual result:
--------------
Warning: simplexml_load_file() [function.simplexml-load-file]: Unable to access E:/php-5.0.1-Win32/../etc/catalog