Re: Fix overflow in DecodeInterval

Ok, so I've attached a patch with my final unprompted changes. It
contains the following two changes:

1. I found some more overflows with the ISO8601 formats and have
included some fixes.
2. I reverted the overflow checks for the seconds field. It's actually a
bit more complicated than I thought. For example consider the following
query:
postgres=# SELECT INTERVAL '0.99999999 min 2147483647 sec';
interval
----------------------
-596523:13:09.000001
(1 row)
This query will overflow the tm_sec field of the struct pg_tm, however
it's not actually out of range for the Interval. I'm not sure the best
way to handle this right now, but I think it would be best to leave it
for a future patch. Perhaps the time related fields in struct pg_tm
need to be changed to 64 bit ints.

- Joe Koshakow