Do not abort if a project has a uninstantiable or abstract class object

instead load is as an object stub and let the user what to do.
Should be enough to close bug #646259
"SIGSEGV in glade_widget_adaptor_object_construct_object loading ui file"

gladeui/glade-object-stub.c

@@ -122,11 +122,17 @@ glade_object_stub_refresh_text (GladeObjectStub *stub)
 {
   GladeObjectStubPrivate *priv = stub->priv;
   gchar *markup;
+  GType type;
 
   if (priv->type == NULL) return;
 
-  markup = g_markup_printf_escaped ("<b>FIXME:</b> Unable to create object with type %s", priv->type);
+  type = g_type_from_name (priv->type);
 
+  if ((type != G_TYPE_INVALID && (!G_TYPE_IS_INSTANTIATABLE (type) || G_TYPE_IS_ABSTRACT (type))))
+    markup = g_markup_printf_escaped ("<b>FIXME:</b> Unable to create uninstantiable object with type %s", priv->type);
+  else
+    markup = g_markup_printf_escaped ("<b>FIXME:</b> Unable to create object with type %s", priv->type);
+  
   gtk_label_set_markup (priv->label, markup);
   gtk_info_bar_set_message_type (GTK_INFO_BAR (stub), GTK_MESSAGE_WARNING);
   g_free (markup);

gladeui/glade-widget.c

@@ -3801,13 +3801,15 @@ glade_widget_read (GladeProject * project,
     {
       if ((id = glade_xml_get_property_string_required (node, GLADE_XML_TAG_ID, NULL)))
         {
+          GType type;
           /* 
            * Create GladeWidget instance based on type. 
            */
-          if ((adaptor = glade_widget_adaptor_get_by_name (klass)) != NULL)
+          if ((adaptor = glade_widget_adaptor_get_by_name (klass)) &&
+              (type = glade_widget_adaptor_get_object_type (adaptor)) &&
+              G_TYPE_IS_INSTANTIATABLE (type) &&
+              G_TYPE_IS_ABSTRACT (type) == FALSE)
             {
-	      
-		  
               /* Internal children !!! */
               if (internal)
                 {