Description:
------------
Garbage collection works in an unexpected way for me,
when there're crossed references. I discovered it working with large 
databases, Apache crashes sometimes : the thread hangs and 
after /etc/init.d/apache2 restart, it continues working.

Another thing : the only way to get track of references is 
debug_zval_dump (of course it can be done manually) and huge strings 
must be parsed. Further, when mixing true (&) and "php" references 
it's no more possible... or is it?

Only a tought...

Thanks

Reproduce code:
---------------
class a {
	public function __destruct() {
		echo 'destr<br>' ;
	}
}

$a = new a ;
$a -> v = new a ;
$a -> w = new a ;
$a -> v -> w = $a -> w ;
$a -> w -> v = $a -> v ;

unset ($a) ;
echo 'fin<br>' ;
exit ;

Expected result:
----------------
destr
destr
destr
fin

Actual result:
--------------
destr
fin
destr
destr