Fix a few memory leaks wrt to translations

Pointed out in https://bugzilla.gnome.org/show_bug.cgi?id=699016
The fix here is slightly different. We make
_gtk_builder_parser_translate return a const char * instead of
a dup'ed string, and fix up the callers.

gtk/gtkscale.c

@@ -1880,7 +1880,7 @@ gtk_scale_buildable_custom_finished (GtkBuildable *buildable,
   if (strcmp (tagname, "marks") == 0)
     {
       GSList *m;
-      gchar *markup;
+      const gchar *markup;
 
       marks_data = (MarksSubparserData *)user_data;