merge 5.1 => 5.5

sql/sql_lex.cc

@@ -1760,6 +1760,7 @@ void st_select_lex::init_query()
   ref_pointer_array= 0;
   select_n_where_fields= 0;
   select_n_having_items= 0;
+  n_child_sum_items= 0;
   subquery_in_having= explicit_limit= 0;
   is_item_list_lookup= 0;
   first_execution= 1;