pgsql: Make the log output of 'vxid' between csvlog and stderr/syslog

Log Message:
-----------
Make the log output of 'vxid' between csvlog and stderr/syslog
consistent. Currently, in csvlog, vxid of an auxiliary process isn't
displayed. On the other hand, in stderr/syslog, invalid vxid (-1/0) of
that is displayed.

Fujii Masao

Modified Files:
--------------
    pgsql/src/backend/utils/error:
        elog.c (r1.210 -> r1.211)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c?r1=1.210&r2=1.211)