Updated the fix for user defined attributes overwriting builtins.

More appropriate fix for the merge: https://github.com/sequelize/sequelize/pull/5219
Now uses hasOwnProperty to more accurately check if the user attribute
matches a builtin.

lib/instance.js

@@ -196,10 +196,8 @@ Instance.prototype.get = function(key, options) { // testhint options:none
         return this.dataValues[key];
       }
     }
-		if (this.dataValues) {
 		return this.dataValues[key];
   }
-  }
 
   if (this._hasCustomGetters || (options && options.plain && this.$options.include) || (options && options.clone)) {
     var values = {}

lib/model.js

@@ -925,7 +925,7 @@ Model.prototype.refreshAttributes = function() {
   this.Instance.prototype._hasCustomSetters = Object.keys(this.Instance.prototype._customSetters).length;
 
   Object.keys(attributeManipulation).forEach((function(key){
-    if (this.Instance.prototype[key] !== undefined) {
+    if (Instance.prototype.hasOwnProperty(key)) {
       this.sequelize.log("Not overriding built-in method from model attribute: " + key);
       return;
     }