Re: Join removal and attr_needed cleanup

We are encountering this issue which results in poor planning for some 
views.

Some examples to illustrate the issue:

-- setup
create table foo as
   select id1, id2
     from generate_series(1, 100) id1,
          generate_series(1, 100) id2;
alter table foo add unique (id1, id2);

-- join elimination works as expected
explain (costs off)
   select a.*
     from foo a
       left join foo b on (b.id1, b.id2) = (a.id1, a.id2)
       left join foo c on (c.id1, c.id2) = (a.id1, a.id2);
                                        -- ^^^^^^^^^^^^^^
--     QUERY PLAN
-- -------------------
--  Seq Scan on foo a

-- join elimination works as expected
explain (costs off)
   select a.*
     from foo a
       left join foo b on (b.id1, b.id2) = (a.id1, a.id2)
       left join foo c on (c.id1, c.id2) = (b.id1, b.id2);
                                        -- ^^^^^^^^^^^^^^
--     QUERY PLAN
-- -------------------
--  Seq Scan on foo a

-- join elimination fails
-- expect both b and c to be eliminated, but b remains
explain (costs off)
   select a.*
     from foo a
       left join foo b on (b.id1, b.id2) = (a.id1, a.id2)
       left join foo c on (c.id1, c.id2) = (a.id1, b.id2);
                                        -- ^^^^^^^^^^^^^^
--                      QUERY PLAN
-- ----------------------------------------------------
--  Hash Left Join
--    Hash Cond: ((a.id1 = b.id1) AND (a.id2 = b.id2))
--    ->  Seq Scan on foo a
--    ->  Hash
--          ->  Seq Scan on foo b