BGE Python API

CListValue fixes
- Disable changing CValueLists that the BGE uses internally (scene.objects.append(1) would crash when drawing)
- val=clist+list would modify clist in place, now return a new value.
- clist.append([....]), was working like extend.
- clist.append(val) didnt work for most CValue types like KX_GameObjects.

Other changes
- "isValid" was always returning True.
- Set all errors for invalid proxy access to PyExc_SystemError (was using a mix of error types)
- Added PyObjectPlus::InvalidateProxy() to manually invalidate, though if python ever gains access again, it will make a new valid proxy. This is so removing an object from a scene can invalidate the object even if its stored elsewhere in a CValueList for eg.

source/gameengine/Expressions/PyObjectPlus.h

@@ -451,6 +451,8 @@ public:
 	static PyObject *GetProxy_Ext(PyObjectPlus *self, PyTypeObject *tp);
 	static PyObject *NewProxy_Ext(PyObjectPlus *self, PyTypeObject *tp, bool py_owns);
 	
+	void	InvalidateProxy();
+	
 	/**
 	 * Makes sure any internal data owned by this class is deep copied.
 	 */