No migration path for MONEY

Folks,

Bug reported off IRC:

MONEY Type cannot be cast to any other type, preventing migration from this
depreciated data type.

Affects: 7.2.3, 7.3.1
Frequency: 100% Reproducable
Effect When Occurring: Unable to convert, query data
Difficulty of Fix: Easy, probably
Certianty of Diagnosis: 100%

On both 7.2.3 and 7.3.1 all of the following statements will fail:

select cast('40.00'::MONEY as NUMERIC);
select cast('40.00'::MONEY as DOUBLE);
select cast('40.00'::MONEY as VARCHAR);
select "numeric"('40.00'::MONEY);
select to_char('40.00'::MONEY, '99999999999.9999');

This means that someone who has inherited or upgarded a 6.5 database with
MONEY columns has no way to migrate them to NUMERIC columns other than an
external language script or dump and reload from COPY file.

I propose that we need to restore the CAST(MONEY AS NUMERIC) function so that
users can migrate old databases to the new data type. In later versions of
postgres, I suggest that MONEY be abandoned as a true data type and instead
become a DOMAIN of NUMERIC for those converting.

--
-Josh Berkus
Aglio Database Solutions
San Francisco