Description:
------------
When unserialize calls __autoload() and this dosn't load the required class unserialize returns an object that doesn't behave like object; var_dump displays it as an object but is_object gives false.

Reproduce code:
---------------
function __autoload($class_name)
{
	
}

var_dump($o = unserialize('O:1:"X":0:{}'));
var_dump(is_object($o));

Expected result:
----------------
object(__PHP_Incomplete_Class)#1 (1) {
  ["__PHP_Incomplete_Class_Name"]=>
  string(1) "X"
}
bool(true)




Actual result:
--------------
object(__PHP_Incomplete_Class)#1 (1) {
  ["__PHP_Incomplete_Class_Name"]=>
  string(1) "X"
}
bool(false)