convert internal properties into private

Author: tiagoschenkel

src/org/osflash/signals/SlotList.ts

@@ -12,6 +12,11 @@ export class SlotList {
      */
     public static NIL: SlotList = new SlotList(null, null);
 
+    // Although those variables are not const, they would be if AS3 would handle it correctly.
+    private head: ISlot;
+    private tail: SlotList;
+    private nonEmpty: boolean = false;
+
     /**
      * Creates and returns a new SlotList object.
      *
@@ -42,11 +47,6 @@ export class SlotList {
         }
     }
 
-    // Although those variables are not const, they would be if AS3 would handle it correctly.
-    public head: ISlot;
-    public tail: SlotList;
-    public nonEmpty: boolean = false;
-
     /**
      * The number of slots in the list.
      */