* return an instance of the NullEngine on engine loading failure; this way applets don't have to test for engine existence and can just assume something gets returned
* DataEngine::isValid() in case someone really cares to know whether they have a non-functional engine (e.g. the NullEngine)
svn path=/trunk/KDE/kdebase/workspace/lib/plasma/; revision=670900
* errorCode is no longer used
* get the debug output in line with similar msgs in plasma
svn path=/trunk/KDE/kdebase/workspace/plasma/lib/; revision=668017
