Merge with 4.0 (Fix bug in LEFT JOIN and EXPLAIN on empty table)

mysql-test/r/explain.result

@@ -1,5 +1,8 @@
 drop table if exists t1;
 create table t1 (id int not null, str char(10), unique(str));
+explain select * from t1;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	system	NULL	NULL	NULL	NULL	0	const row not found
 insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
 select * from t1 where str is null;
 id	str