Description:
------------
PHP crashes when passing large object ( with __toString() method ) to string functions (like substr(), urlencode() etc.)

Test script:
---------------
<?php

class Foo
{


protected $obj;

function rec($i = 0, $obj)
{
	$this -> obj = $obj;

	// >5603 - segmentation fault or zend_mm_heap corrupted
	// With some values can work as expected 
	if ( $i < 15604) {  
		$this -> rec(++$i, $this);
	}
	
}

function __toString()
{
	$this -> rec(0, $this);
	return "Hello, world!";
}

}


$foo = new Foo();

substr($foo, 0, 5);

// This is ok
//echo "\nHello!\n";

// But if we begin using variables "zend_mm_heap corrupted" or "Segmentation Fault"
$a = "aaaaa\n";
echo $a;

?>

Expected result:
----------------
Expecting correct appication exit

Actual result:
--------------
"Segmentation Fault" or "zend_mm_heap corrupted" errors