EvenId const fixes.

src/simulator/event-id.cc

@@ -45,12 +45,12 @@ EventId::Cancel (void)
     }
 }
 bool 
-EventId::IsExpired (void)
+EventId::IsExpired (void) const
 {
   return Simulator::IsExpired (*this);
 }
 bool 
-EventId::IsRunning (void)
+EventId::IsRunning (void) const
 {
   return !IsExpired ();
 }

src/simulator/event-id.h

@@ -44,8 +44,8 @@ public:
    * method.
    * \returns true if the event has expired, false otherwise.
    */
-  bool IsExpired (void);
-  bool IsRunning (void);
+  bool IsExpired (void) const;
+  bool IsRunning (void) const;
 public:
   /* The following methods are semi-private
    * they are supposed to be invoked only by