pgsql: In the integer-datetimes case, date2timestamp and

Log Message:
-----------
In the integer-datetimes case, date2timestamp and date2timestamptz need
to check for overflow because the legal range of type date is actually
wider than timestamp's.  Problem found by Neil Conway.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        date.c (r1.135 -> r1.136)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/date.c?r1=1.135&r2=1.136)