Description:
------------
array_key_exists() may take object as second parameter and
in such case I think it should use __isset() magic function of the object (if any), but it seems not to do so.
The  isset() and array_key_exists() may return different results for the same object, which is not good :)

Reproduce code:
---------------
class TestObject
{
	function __isset($nm)
	{
		return true;
	}
}

$A = new TestObject();

var_dump(array_key_exists('test', $A));
var_dump(isset($A->test));

Expected result:
----------------
true
true

Actual result:
--------------
false
true