Fixes for binary protocol (complement to last push)

Changed timestamp to return string in YYYY-MM-DD HH:MM:SS format.
DATE_ADD() and related functions now returns correct DATE/DATETIME type depending on argument types.
Now all tests passes, still some work left to remove warnings in log files from mysql-test-run

sql/sql_class.cc

@@ -520,6 +520,7 @@ bool select_send::send_data(List<Item> &items)
   if (unit->offset_limit_cnt)
   {						// using limit offset,count
     unit->offset_limit_cnt--;
+    return 0;
   }
 
   List_iterator_fast<Item> li(items);