pgsql: In a machine where INT64_IS_BUSTED, we can only support 32-bit

Log Message:
-----------
In a machine where INT64_IS_BUSTED, we can only support 32-bit values
for int8 and related types.  However we might be talking to a client
that has working int64; so pq_getmsgint64 really needs to check the
incoming value and throw an overflow error if we can't represent it
accurately.

Modified Files:
--------------
    pgsql/src/backend/libpq:
        pqformat.c (r1.37 -> r1.38)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pqformat.c.diff?r1=1.37&r2=1.38)