money type overflow checks

The input function of the money type has no overflow checks:

=> select '12345678901234567890'::money;
            money
-----------------------------
 -$13,639,628,150,831,692.72
(1 row)

The tests in the regression test file money.sql are bogus because they
only test the overflow checks of the bigint type before the cast.

Here is a patch that adds appropriate checks and tests.  We could
probably remove the bogus tests.

(Is checking for < 0 a valid overflow check?  We save the sign until the
very end, so it ought to work.  The code in int8.c works differently there.)

--
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services