Description:
------------
When I unset an array containing object, the memory is not freed as expected. Too much memory is still used.

Reproduce code:
---------------
<?
ini_set('memory_limit','300M');
class a {
}

echo memory_get_usage()."\n";
$a=array();
for ($i=0; $i<=1000000; $i++) {
	$a[]= new a();
}
echo memory_get_usage()."\n";
unset($a);
echo memory_get_usage()."\n";
?>

Expected result:
----------------
325776
230042304
circa 325776

Actual result:
--------------
325776
230042304
33977912