difference between INSERT_IN_PROGRESS and DELETE_IN_PROGRESS for
tuples inserted and then deleted by a concurrent transaction.
Example of bug:
regression=# create table foo (f1 int);
CREATE TABLE
regression=# begin;
BEGIN
regression=# insert into foo values(1);
INSERT 195531 1
regression=# delete from foo;
DELETE 1
regression=# insert into foo values(1);
INSERT 195532 1
regression=# create unique index fooi on foo(f1);
ERROR:  could not create unique index
DETAIL:  Table contains duplicated values.