Include the name which was the cause of the IllegalArgumentException while try to add a handler to the pipeline

src/main/java/org/jboss/netty/channel/DefaultChannelPipeline.java

@@ -685,7 +685,7 @@ public class DefaultChannelPipeline implements ChannelPipeline {
 
     private void checkDuplicateName(String name) {
         if (name2ctx.containsKey(name)) {
-            throw new IllegalArgumentException("Duplicate handler name.");
+            throw new IllegalArgumentException("Duplicate handler name " + name);
         }
     }