Update release notes

Add a warning about the change in GtkBuilders id/name handling.

README.in

@@ -37,13 +37,9 @@ Release notes for 2.20
   which are doing so may need some adjustments, since the addition of the
   message area changed the internal widget hierarchy.
 
-* GDK will now set all matching virtual modifiers in the state field of
-  key events. Depending on your X modifier map, this can lead to more bits
-  in the state field being set than before. If you are manually matching
-  key events against key/modifier combinations you should make sure that
-  you properly mask away irrelevant parts of the state field. The
-  gdk_keymap_map_virtual_modifiers() function can help with matching
-  against virtual modifiers.
+* GtkBuilder no longer sets the "name" property of widgets to the ID
+  attribute of the <object>. Use gtk_buildable_get_name() instead of
+  gtk_widget_get_name() to obtain the ID.
 
 Release notes for 2.18
 ======================

docs/reference/gtk/tmpl/gtkbuilder.sgml

@@ -116,6 +116,12 @@ allows the application to retrieve them from the builder with
 gtk_builder_get_object(). An id is also necessary to use the
 object as property value in other parts of the UI definition.
 </para>
+<note><para>Prior to 2.20, GtkBuilder was setting the "name"
+property of constructed widgets to the "id" attribute. In GTK+
+2.20 or newer, you have to use gtk_buildable_get_name() instead
+of gtk_widget_get_name() to obtain the "id", or set the "name"
+property in your UI definition.
+</para></note>
 <para>
 Setting properties of objects is pretty straightforward with
 the &lt;property&gt; element: the "name" attribute specifies