Fix various SWIG warnings

src/python/swig/event.i

@@ -44,8 +44,8 @@
 
 void create(PyObject *object, Tick when);
 
-class Event;
-class CountedDrainEvent : public Event {
+class CountedDrainEvent
+{
   public:
     void setCount(int _count);
 };

src/python/swig/range.i

@@ -28,6 +28,8 @@
  * Authors: Nathan Binkert
  */
 
+%rename(assign) *::operator=;
+
 %include "base/range.hh"
 %include "sim/host.hh"