[appserver-io/appserver] Timing issues with class declaration synchronisation

[wick-ed]

With certain timings there is a problem with synchronizing of the class declarations in between thread contexts. Therefor certain classes do not exist in child threads but cannot be loaded due to our architecture.

Error message:

[16-Jul-2015 14:56:18 Europe/Berlin] PHP Fatal error:  AppserverIo\Appserver\Core\DgClassLoader::loadClass(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "AppserverIo\Appserver\Core\StackableStructureMap" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition  in /opt/appserver/src/AppserverIo/Appserver/Core/DgClassLoader.php on line 348

[wick-ed]

Closed with this PR