Finding all 8.4->9.x incompatible PL/pgSQL functions with conflicting parameter/column names causing "column reference ... is ambiguous" errors

I'm upgrading from 8.4 to 9.1, and have a lot of PL/pgSQL functions which
works in 8.4, but when called, throws an error in 9.1.

Example:

CREATE TABLE mytable (id serial not null primary key, value text);

INSERT INTO mytable (id, value) VALUES (1, 'foo');
INSERT INTO mytable (id, value) VALUES (2, 'bar');

CREATE OR REPLACE FUNCTION myfunc(id int) RETURNS TEXT AS $$
DECLARE
value text;
BEGIN
SELECT mytable.value INTO value FROM mytable WHERE mytable.id = id;
RETURN value;
END;
$$ LANGUAGE plpgsql;

SELECT myfunc(1);
SELECT myfunc(2);

This returns "foo" and "bar" like expected in 8.4, but in 9.1 I get "column
reference "id" is ambiguous", "It could refer to either a PL/pgSQL variable
or a table column.".

This is of course easy to fix by qualifying id with the name of the
function:

-SELECT mytable.value INTO value FROM mytable WHERE mytable.id = id;
+SELECT mytable.value INTO value FROM mytable WHERE mytable.id = myfunc.id;

The problem is, how can I find all functions which have this problem?

You don't get this error when creating the functions, only when running
them and hitting a statement where there is a conflict.

Would it be possible to somehow automatically scan through all functions
and getting a list of the functions which have this problem?

Thanks!

Best regards,

Joel Jacobson