window: make sidebar menus work with latest GtkPlacesSidebar

Now GtkPlacesSidebar uses GMenu, so the API for the populate-popup
signal changed. Update acordingly to make context menus work again.

src/nautilus-window.ui

@@ -32,6 +32,7 @@
                 <child>
                   <object class="GtkPlacesSidebar" id="places_sidebar">
                     <property name="visible">True</property>
+                    <property name="populate-all">True</property>
                   </object>
                   <packing>
                     <property name="pack_type">start</property>