Memory leaks in record_out and record_send

I looked into the problem complained of here:
http://archives.postgresql.org/pgsql-general/2012-11/msg00279.php
which turns out to have nothing to do with joins and everything to do
with the fact that record_out() leaks memory like mad. It leaks both
the strings returned by the per-column output functions and any column
values that have to be detoasted. You can easily reproduce this with
an example like

create table leak (f1 int, f2 text);

insert into leak select x, 'foo' from generate_series(1,1000000) x;

select leak from leak;

The attached patch against HEAD fixes this, as well as a similar
leakage in record_send(). The added code is lifted directly from
printtup() so it's not adding any new assumptions to the system.

I wonder though if we ought to think about running output functions in
a short-lived memory context instead of the executor's main context.
We've considered that before, I think, and it's always been the path
of least resistance to fix the output functions instead --- but there
will always be another leak I'm afraid.

OTOH I can't see trying to back-patch a solution like that. If we want
to fix this in the back branches (and note the complaint linked above is
against 8.3), I think we have to do it as attached.

Thoughts?

regards, tom lane