Improve the following.

 =# create table t (id int4 unique);
NOTICE:  CREATE TABLE/UNIQUE will create implicit index 't_id_key' for table 't'
 =# begin;
 query: drop table t;
NOTICE:  Caution: DROP TABLE cannot be rolled back, so don't abort now
NOTICE:  Caution: DROP INDEX cannot be rolled back, so don't abort now
 =# rollback;
 =# drop table t;
NOTICE:  mdopen: couldn't open t: No such file or directory
NOTICE:  RelationIdBuildRelation: smgropen(t): No such file or directory
NOTICE:  mdopen: couldn't open t: No such file or directory
NOTICE:  mdopen: couldn't open t: No such file or directory
NOTICE:  mdopen: couldn't open t_id_key: No such file or directory
NOTICE:  RelationIdBuildRelation: smgropen(t_id_key): No such file or directory
NOTICE:  mdopen: couldn't open t: No such file or directory
NOTICE:  RelationIdBuildRelation: smgropen(t): No such file or directory
NOTICE:  mdopen: couldn't open t: No such file or directory
ERROR:  cannot open relation t