MATSim Code

- Streaming in PopulationImpl must now be enabled with the method PopulationImpl.setIsStreaming(true) and can no longer be done in the constructor. This is partly due to the fact that "new PopulationImpl()" (without arguments in the Controler) already always created a non-streaming PopulationImpl, and partly due to the fact that with the recent change to ScenarioImpl (which always creates a non-streaming PopulationImpl internally) streaming would not be usable together with ScenarioImpl.