Bug #605: timestamp(timestamp('a timestamp)) no longer works

Andrew McMillan (andrew(at)catalyst(dot)net(dot)nz) reports a bug with a severity of 3
The lower the number the more severe it is.

Short Description
timestamp(timestamp('a timestamp)) no longer works

Long Description
In version 7.2 it seems that I can't reduntantly cast value to timestamp if it is already a timestamp.

I do this reasonably often in my code by way of being paranoid that I might have a date, or a time, where I for sure _really_ want it to be a timestamp...

It's cleaning up some bugs in my code, I suppose, but I kind of like making it explicit to people who might come along after me :-)

Sample Code
Here's the broken query:

pcnz=# select timestamp('2002-03-01'::timestamp);
ERROR: parser: parse error at or near "'"
pcnz=# select version();
version
-------------------------------------------------------------
PostgreSQL 7.2 on i686-pc-linux-gnu, compiled by GCC 2.95.4
(1 row)

I notice that int4(int4()) still works:

pcnz=# select int4( '777'::int4 );
int4
------
777
(1 row)

A couple of older versions where this worked:

pcnz=# select timestamp('2002-03-01'::timestamp);
timestamp
------------------------
2002-03-01 00:00:00+13
(1 row)

pcnz=# select version();
version
---------------------------------------------------------------
PostgreSQL 7.0.3 on i686-pc-linux-gnu, compiled by gcc 2.95.2
(1 row)

stimulus=# select timestamp('2002-03-01'::timestamp);
timestamp
------------------------
2002-03-01 00:00:00+13
(1 row)

stimulus=# select version();
version
---------------------------------------------------------------
PostgreSQL 7.1.3 on i686-pc-linux-gnu, compiled by GCC 2.95.4
(1 row)

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