removing a non-linear behaviour from ID/IDREF raised by Petr Pajas. Call

* valid.c: removing a non-linear behaviour from ID/IDREF raised
  by Petr Pajas. Call xmlListAppend instead of xmlListInsert in
  xmlAddRef
Daniel
diff --git a/valid.c b/valid.c
index b0c2507..33a2a9a 100644
--- a/valid.c
+++ b/valid.c
@@ -2798,7 +2798,8 @@
             return(NULL);
         }
     }
-    xmlListInsert(ref_list, ret);
+/*    xmlListInsert(ref_list, ret); */
+    xmlListAppend(ref_list, ret);
     return(ret);
 }