tuplesort_putdatum() does not account for tuple memory

Hi hackers,

Memory allocated for copied pass-by-reference Datums was not accounted
against work_mem because tuplesort_putdatum() passed a hardcoded tuplen
of 0 to tuplesort_puttuple_common(). Function free_sort_tuple() adjusts
the accounting by the amount actually allocated, so freeing such a
tuple subtracts an amount that was never added.

This was introduced in 6ed83d5fa55, which switched non-bounded sorts to
bump contexts. That commit correctly changed the other tuplesort_put*()
functions to compute the size, leaving only this one passing hardcoded
0.

So currently:

1) Bounded datum sorts are misreported. With work_mem = 4MB:

EXPLAIN ANALYZE SELECT md5(i::text) AS hash 
FROM generate_series(1,100000) i
ORDER BY hash LIMIT 5;

master: Sort Method: still in progress Memory: 0kB
patched: Sort Method: top-N heapsort Memory: 25kB

2) work_mem is not enforced against the tuple data, and hold more data
than allowed before spilling With work_mem = 4MB:

EXPLAIN ANALYZE SELECT md5(i::text) AS hash 
FROM generate_series(1,100000) i
ORDER BY hash;

master: Sort Method: quicksort Memory: 3073kB
patched: Sort Method: external merge Disk: 3920kB

The attached patch computes tuplen the way the tuplesort_put*()
variants do.

Thanks,
Mario