Fix isEmpty() and count()

isEmpty() need not rely on peek(which is intended for consumer use) and instead compare head to tail.
count() should stop counting at max int to avoid wrap.

akka-actor/src/main/java/akka/dispatch/AbstractNodeQueue.java

@@ -57,12 +57,12 @@ public abstract class AbstractNodeQueue<T> extends AtomicReference<AbstractNodeQ
     }
 
     public final boolean isEmpty() {
-        return peek() == null;
+        return Unsafe.instance.getObjectVolatile(this, tailOffset)) == get();
     }
 
     public final int count() {
         int count = 0;
-        for(Node<T> n = peekNode();n != null; n = n.next())
+        for(Node<T> n = peekNode();n != null && count < Integer.MAX_VALUE; n = n.next())
           ++count;
         return count;
     }