Description:
------------
Cannot catch a simple loading error when using simplexml_load_string() loading an invalid xml string.

I understand that that E_WARNING, E_ERROR etc are not exceptions but realisticlly, I expect a loading function to throw an exception when it fails to load a object, not a uncatchable "warning". It also be invalid to say this error class is a "warning" as it is most definitely an error.  

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

try {
        $x = simplexml_load_string("adfasdf");
        print_r($x);
}
catch (Exception $e) {
        echo "toast";
}

?>

Expected result:
----------------
toast

Actual result:
--------------
Warning: simplexml_load_string(): Entity: line 1: parser error : Start tag expected, '<' not found in...

Warning: simplexml_load_string(): adfasdf in...

Warning: simplexml_load_string(): ^ in...