Interval output bug in HAVE_INT64_TIMESTAMP

Seems to me there's a bug in HEAD (and probably old branches
as well) when compiled with HAVE_INT64_TIMESTAMP. As shown below
It sometimes shows things like "-6.-70 secs" where 8.3
showed "-6.70 secs".

I think the attached one-liner patch fixes this, as well as
another roundoff regression between HEAD and 8.3.

Ron Mayer

================================================================================
== ON HEAD
================================================================================
regression=# set datestyle to sql;
SET
regression=# select '-10 mons -3 days +03:55:06.70'::interval;
interval
----------------------------------------------------
@ 10 mons 3 days -3 hours -55 mins -6.-70 secs ago
(1 row)

regression=# select '1 year 2 mons 3 days 04:05:06.699999'::interval;
interval
-------------------------------------------------
@ 1 year 2 mons 3 days 4 hours 5 mins 6.69 secs
(1 row)

================================================================================
== ON 8.3
================================================================================
pg83=# set datestyle to sql;
SET
pg83=# select '-10 mons -3 days +03:55:06.70'::interval;
interval
---------------------------------------------------
@ 10 mons 3 days -3 hours -55 mins -6.70 secs ago
(1 row)

pg83=# select '1 year 2 mons 3 days 04:05:06.699999'::interval;
interval
-------------------------------------------------
@ 1 year 2 mons 3 days 4 hours 5 mins 6.70 secs
(1 row)