Description:
------------
There are two objects of the same class. Both objects has a property. There are
circular object reference: $a->prop === $b && $b->prop === $a. The class has
a __clone() handler which clones object in that property.

So, clonning such object cause segfault.

Yes, described architecture is ugly, but this is just for test.

Test code:

----
    class A {
        public $prop;

        public function __clone() {
            $this->prop = clone $this->prop;
        }
    }

    // create two objects
    $a = new A();
    $b = new A();

    // create circular reference
    $b->prop = $a;
    $a->prop = $b;

    // see short dump with *RECURSION* marker
    print_r($a);

    // now make a problem
    $c = clone $a;

    // never will reach here
    print_r($c);
----

5.5.0.a2, 5.4.11, 5.3.20 and 5.2.17 crashes with segfault. It is infinite
recursion. Also Fatal Error can be emited about memory allocation when small
memory_limit is set (1M for example).

Unlimited recursion for a simple function cause a fatal error, so the bug always should cause the same fatal error.

Test script:
---------------
class A {
    public $prop;

    public function __clone() {
        $this->prop = clone $this->prop;
    }
}

$a = new A();
$b = new A();

$b->prop = $a;
$a->prop = $b;

print_r($a);

$c = clone $a;
print_r($c);

Expected result:
----------------
A Object
(
    [prop] => A Object
        (
            [prop] => A Object
 *RECURSION*
        )

)

Fatal error: Allowed memory size of ... bytes exhausted (tried to allocate ... bytes)

Actual result:
--------------
A Object
(
    [prop] => A Object
        (
            [prop] => A Object
 *RECURSION*
        )

)
Segmentation fault (core dumped)