don't translate error message and replace console log with exception

lib/OpenLayers/Map.js

@@ -8,8 +8,6 @@
  * @requires OpenLayers/Util.js
  * @requires OpenLayers/Events.js
  * @requires OpenLayers/Tween.js
- * @requires OpenLayers/Console.js
- * @requires OpenLayers/Lang.js
  */
 
 /**
@@ -946,12 +944,10 @@ OpenLayers.Map = OpenLayers.Class({
     * layer - {<OpenLayers.Layer>} 
     */    
     addLayer: function (layer) {
-        for(var i=0, len=this.layers.length; i <len; i++) {
+        for(var i = 0, len = this.layers.length; i < len; i++) {
             if (this.layers[i] == layer) {
-                var msg = OpenLayers.i18n('layerAlreadyAdded', 
-                                                      {'layerName':layer.name});
-                OpenLayers.Console.warn(msg);
-                return false;
+                throw new Error("You tried to add the layer: " + layer.name +
+                                " to the map, but it has already been added");
             }
         }
         if (this.events.triggerEvent("preaddlayer", {layer: layer}) === false) {
@@ -960,7 +956,6 @@ OpenLayers.Map = OpenLayers.Class({
         if(this.allOverlays) {
             layer.isBaseLayer = false;
         }
-
         
         layer.div.className = "olLayerDiv";
         layer.div.style.overflow = "";