Redefine the existing class if it's resolved

lib/model-builder.js

@@ -107,7 +107,9 @@ ModelBuilder.prototype.define = function defineClass(className, properties, sett
     // Check if there is a unresolved model with the same name
     var ModelClass = this.models[className];
 
-    if(!ModelClass) {
+    // Create the ModelClass if it doesn't exist or it's resolved (override)
+    // TODO: [rfeng] We need to decide what names to use for built-in models such as User.
+    if(!ModelClass || !ModelClass.settings.unresolved) {
         // every class can receive hash of data as optional param
         ModelClass = function ModelConstructor(data, dataSource) {
             if(!(this instanceof ModelConstructor)) {