Validation in to_date()

to_date() doesn't check the date range, which results in unreadable
data like this.

foo=# create table t as select to_date('9999-12-10 BC', 'YYYY-MM-DD
BC')::timestamp;
SELECT 1
foo=# table t;
ERROR:  timestamp out of range

Attached is to add IS_VALID_JULIAN() as we do like in date_in().  I
think to_date() should follow it because it is the entrance place to
check sanity.

Thanks,
--
Hitoshi Harada