pgsql: Fix integral timestamps so the output is consistent in all cases

Log Message:
-----------
Fix integral timestamps so the output is consistent in all cases to
round:

select interval '0:0:0.7', interval '@ 0.70 secs', interval '0.7
seconds';

Ron Mayer

Modified Files:
--------------
pgsql/src/backend/utils/adt:
datetime.c (r1.193 -> r1.194)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/datetime.c?r1=1.193&r2=1.194)