Backport parts of ipywidgets#3

IPython/html/static/widgets/js/widget.js

@@ -24,6 +24,7 b' define(["widgets/js/manager",'
              *      An ID unique to this model.
              * comm : Comm instance (optional)
              */
+            WidgetModel.__super__.constructor.apply(this);
             this.widget_manager = widget_manager;
             this.state_change = Promise.resolve();
             this._buffered_state_diff = {};
@@ -32,6 +33,13 b' define(["widgets/js/manager",'
             this.state_lock = null;
             this.id = model_id;
             this.views = {};
+
+            // Force backbone to think that the model has already been
+            // synced with the server.  As of backbone 1.1, backbone
+            // ignores `patch` if it thinks the model has never been
+            // pushed.
+            this.isNew = function() { return false; };
+
             this._resolve_received_state = {};
 
             if (comm !== undefined) {

IPython/html/tests/widgets/widget.js

@@ -115,7 +115,7 b' casper.notebook_test(function () {'
     var multiset = {};
     multiset.index = this.append_cell(
         'from IPython.utils.traitlets import Unicode, CInt\n' +
-        'class MultiSetWidget(widgets.Widget):\n' +
+        'class MultiSetWidget(widgets.DOMWidget):\n' +
         '    _view_name = Unicode("MultiSetView", sync=True)\n' +
         '    a = CInt(0, sync=True)\n' +
         '    b = CInt(0, sync=True)\n' +