pg_waldump and PREPARE

Hi,

pg_waldump report no detail information about PREPARE TRANSACTION record,
as follows.

    rmgr: Transaction len (rec/tot):    250/   250, tx:        485,
lsn: 0/020000A8, prev 0/02000060, desc: PREPARE

I'd like to modify pg_waldump, i.e., xact_desc(), so that it reports
detail information like GID, as follows. Attached patch does that.
This would be helpful, for example, when diagnosing 2PC-related
trouble by checking the status of 2PC transaction with the specified GID.
Thought?

    rmgr: Transaction len (rec/tot):    250/   250, tx:        485,
lsn: 0/020000A8, prev 0/02000060, desc: PREPARE gid abc: 2004-06-17
05:26:27.500240 JST

I will add this to next CommitFest page.

Regards,

-- 
Fujii Masao