MWL#121-125 DS-MRR improvements

- Address Monty's review feedback, part 5

mysql-test/r/innodb_mrr.result

@@ -168,6 +168,7 @@ c-1020=w	filler
 c-1021=w	filler
 c-1022=w	filler
 c-1023=w	filler
+drop table if exists t4;
 create table t4 (a varchar(10), b int, c char(10), filler char(200),
 key idx1 (a, b, c));
 insert into t4 (filler) select concat('NULL-', 15-a) from t2 order by a limit 15;