Fix showing XID of a spectoken lock in an incorrect field of pg_locks view.

Hi,

I realized that pg_locks view shows the transaction id of a
speculative token lock in the database field:

postgres(1:509389)=# select * from pg_locks where locktype = 'spectoken';
locktype | database | relation | page | tuple | virtualxid |
transactionid | classid | objid | objsubid | virtualtransaction | pid
| mode | granted | fastpath | waitstart
-----------+----------+----------+------+-------+------------+---------------+---------+-------+----------+--------------------+--------+---------------+---------+----------+-----------
spectoken | 741 | | | | |
| 3 | 0 | 0 | 3/5 | 509314 |
ExclusiveLock | t | f |
(1 row)

It seems to be confusing and the user won't get the result even if
they search it by transactionid = 741. So I've attached the patch to
fix it. With the patch, the pg_locks views shows like:

locktype | database | relation | page | tuple | virtualxid |
transactionid | classid | objid | objsubid | virtualtransaction | pid
| mode | granted | fastpath | waitstart
-----------+----------+----------+------+-------+------------+---------------+---------+-------+----------+--------------------+--------+---------------+---------+----------+-----------
spectoken | | | | | |
746 | | 1 | | 3/4 | 535618 |
ExclusiveLock | t | f |
(1 row)

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com