Description:
------------
__destruct() not called on unset() if one of methods used as callback for set_error_handler() function.

Reproduce code:
---------------
class Sample
{
function __construct() { set_error_hanlder(array(&$this,'OnError')); }
function __destruct () { echo '[DESTRUCT]'; }
function OnError ($a,$b,$c,$d) { echo 'Error'; }
}

$sample = new Sample();

echo '[BEFORE]';
unset($sample);
echo '[AFTER]';

Expected result:
----------------
[BEFORE][DESTRUCT][AFTER]

Actual result:
--------------
[BEFORE][AFTER][DESTRUCT]