Description:
------------
Exception::getTraceAsString, Exception::__toString are not able to properly handle unicode in stack trace. Instead of showing actual argument values it's giving ???? in case value is unicode.

Tested on PHP 5.3 and PHP 5.4.

Test script:
---------------
<?php
function test($arg){
	throw new Exception();
}

try {
	test('тест');
}
catch(Exception $e) {
	echo $e->getTraceAsString();
	echo (string)$e;
}

Expected result:
----------------
d:\web\usr\local\php54>php.exe d:\src\exception_wrong_trace\test.php
#0 D:\src\exception_wrong_trace\test.php(7): test('тест')
#1 {main}exception 'Exception' in D:\src\exception_wrong_trace\test.php:3
Stack trace:
#0 D:\src\exception_wrong_trace\test.php(7): test('тест')
#1 {main}

Actual result:
--------------
d:\web\usr\local\php54>php.exe d:\src\exception_wrong_trace\test.php
#0 D:\src\exception_wrong_trace\test.php(7): test('????')
#1 {main}exception 'Exception' in D:\src\exception_wrong_trace\test.php:3
Stack trace:
#0 D:\src\exception_wrong_trace\test.php(7): test('????')
#1 {main}