* bugfix for BGE python api - SetParent actuator getObject would segfault if the object was not set.
* Added utility function ConvertPythonToGameObject() that can take a GameObject, string or None and set the game object from this since it was being done in a number of places.
* allow setObject(None), since no object is valid for actuators, Python should be able to set this.
* added optional argument for getObject() so it returns the KX_GameObject rather then its name, would prefer this be default but it could break existing games.
Certain actuators (Add Object/Replace Mesh/Scene/Track To) used to always require a target, or they would not influence the scene. If the actuator target is always set from Python, this could be annoying.
