post review changes 2

sql/event_parse_data.cc:
  don't use "not_used" variable
sql/item_timefunc.cc:
  Item_temporal_func::fix_length_and_dec()
  and other changes
sql/item_timefunc.h:
  introducing Item_timefunc::fix_length_and_dec()
sql/share/errmsg.txt:
  don't say "column X" in the error message that used not only for columns

sql/sql_class.cc

@@ -2338,7 +2338,8 @@ bool select_max_min_finder_subselect::send_data(List<Item> &items)
       case DECIMAL_RESULT:
         op= &select_max_min_finder_subselect::cmp_decimal;
         break;
-      default:
+      case ROW_RESULT:
+      case TIME_RESULT:
         // This case should never be choosen
 	DBUG_ASSERT(0);
 	op= 0;