#5084 various improvements

 Handle exceptions in JSON decoding, delay refresh when
 a code 200 occurs, handle channel subscription in the
 library

 define([], function() {
-    var listeners = [];
+    var channels = {};
     var messenger = {
         process: function() {
+            var self = this;
             var url = "/comet/messenger"
             var request =  new XMLHttpRequest();
             var responseLength = 0;
@@ -13,9 +14,7 @@ define([], function() {
                         if (request.responseText) {
                             var newText = request.responseText.substr(responseLength);
                             if (newText.length > 0) {
-                                for (var i=0; i < listeners.length; i++) {
-                                   listeners[i](newText); 
-                                }
+                                self.deliver(newText);
                             }
                             responseLength = request.responseText.length;
                         }
@@ -34,14 +33,33 @@ define([], function() {
             };
             request.send(null);
         },
+        deliver: function(newText) {
+            try {
+                var json = JSON.parse(newText);
+
+                if (json.channel && channels[json.channel]) {
+                    for (var i=0; i < channels[json.channel].length; i++) {
+                       channels[json.channel][i](json); 
+                    }
+                }
+            } catch (err) {
+                console.log('Error processing COMETd message', newText, err);
+            }
+        },
         addListener: function(listener) {
-            listeners.push(listener);
+            this.addListener('ALL', listener);
         },
-        removeListener: function(listener) {
-            var index = listeners.indexOf(listener);
-            if (index > -1) {
-                array.splice(index, 1);
+        addListener: function(channel, listener) {
+            if (!channels[channel]) {
+                channels[channel] = [];
             }
+            channels[channel].push(listener);
+        },
+        removeListener: function(listener) {
+            this.removeListener('ALL', listener);
+        },
+        removeListener: function(channel, listener) {
+            console.log('Remove listener from channel', listener, channel);
         }
     }
     messenger.process();