Description:
------------
It appears that json_decode is less strict in newer versions of PHP, and allows object keys to be single quoted.

Test script:
---------------
$ php -v
PHP 5.5.3 (cli) (built: Aug 21 2013 17:57:15)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
    with Zend OPcache v7.0.3-dev, Copyright (c) 1999-2013, by Zend Technologies
    with Xdebug v2.2.3, Copyright (c) 2002-2013, by Derick Rethans

$ php -r "var_dump(json_decode(\"{'a':1}\"));"
class stdClass#1 (1) {
  public $a =>
  int(1)
}

Expected result:
----------------
json_decode should return NULL and make the error available through json_last_error()

Actual result:
--------------
The string is parsed into an object