7.3.3 ADD COLUMN wierdness

I'm running two different strains of PostgreSQL

7.1.3, which is what our website is running off of now and 7.3.3, which we
hope to move to (sometime).

In 7.1.3 I can say

ALTER TABLE blah ADD COLUMN whatever integer not null;

and as expected, that works fine

on 7.3.3

the same command returns
Adding NOT NULL columns is not implemented.
Add the column, then use ALTER TABLE ... SET NOT NULL.

Hmm, the last time I checked, this should have worked.
Is this a bug or a feature?

If it's a feature, can I turn it off, because this is a hassel.

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