1.x: Subscriber.NOT_SET Long -> long, saves an unboxing per instance (#3919)

Author: akarnokd

src/main/java/rx/Subscriber.java

@@ -33,7 +33,7 @@
 public abstract class Subscriber<T> implements Observer<T>, Subscription {
 
     // represents requested not set yet
-    private static final Long NOT_SET = Long.MIN_VALUE;
+    private static final long NOT_SET = Long.MIN_VALUE;
 
     private final SubscriptionList subscriptions;
     private final Subscriber<?> subscriber;