DDC-3120 - add failing test for un-serialization of an internal PHP class
DDC-3120 - add failing test for un-serialization of an internal PHP class from cached metadata instance
DDC-3120 - metadata should be initialized before attempting new instance creation
DDC-3120 - metadata should be waked up before attempting new instance creation
DDC-3120 - Using `ReflectionClass#newInstanceWithoutConstructor()` also with PHP 5.6+
DDC-3120 - Adding PHP 5.6 to build matrix
Merge pull request #1154 from Ocramius/hotfix/PHP-5.6-serialization-fix

DDC-3120 - PHP 5.6 internal classes/Serializable serialization fix