[query-params-new] Don't watch default model params obj

Subtle bug fix with query-params-new, whereby if you
specified queryParams on your ObjectController but
didn't provide you own model hook, the Ember-supplied
model hook, which returns the params object as the 
model in certain cases, was resulting in that params
object being observed, when definitely should not be,
so we make a copy of the POJO before returning it
as the model

Fixes #4155

packages/ember-routing/lib/system/route.js

@@ -859,7 +859,7 @@ Ember.Route = Ember.Object.extend(Ember.ActionHandler, {
       sawParams = true;
     }
 
-    if (!name && sawParams) { return params; }
+    if (!name && sawParams) { return Ember.copy(params); }
     else if (!name) { return; }
 
     return this.findModel(name, value);

packages/ember/tests/routing/query_params_test.js

@@ -661,4 +661,31 @@ if (Ember.FEATURES.isEnabled("query-params-new")) {
 
 
   });
+
+  test("Defaulting to params hash as the model should not result in that params object being watched", function() {
+    expect(1);
+
+    Router.map(function() {
+      this.route('other');
+    });
+
+    // This causes the params hash, which is returned as a route's
+    // model if no other model could be resolved given the provided
+    // params (and no custom model hook was defined), to be watched,
+    // unless we return a copy of the params hash.
+    App.ApplicationController = Ember.ObjectController.extend({
+      queryParams: ['woot']
+    });
+
+    App.OtherRoute = Ember.Route.extend({
+      model: function(p, trans) {
+        var m = Ember.meta(trans.params.application);
+        ok(!m.watching.woot, "A meta object isn't constructed for this params POJO");
+      }
+    });
+
+    bootApplication();
+
+    Ember.run(router, 'transitionTo', 'other');
+  });
 }