Re: pageinspect: add tuple_data_record()

There's plenty ways it can go horribly wrong. Let's start with something
simple:

BEGIN;
ALTER TABLE ... ADD COLUMN blarg INT;
INSERT ... (blag) VALUES (132467890);
ROLLBACK;

ALTER TABLE ... ADD COLUMN blarg TEXT;

If you now read the table with your function you'll see a dead row that
will re-interpret a int datum as a text datum. Which in all likelyhood
will crash the server.