FieldSelect/FieldStore dependencies, take 2

I had a nagging feeling that commit f3ea3e3e8 was not quite covering
all the bases with respect to what dependencies to record for
FieldSelect/FieldStore nodes: it looked at the result type, but what
about the input type? Just now, while fooling around with domains
over composite, I stumbled across a case that shows what's missing:

regression=# create type complex as (r float8, i float8);
CREATE TYPE
regression=# create domain dcomplex as complex check((value).r > (value).i);
CREATE DOMAIN
regression=# select pg_get_constraintdef((select max(oid) from pg_constraint));
pg_get_constraintdef
---------------------------------
CHECK (((VALUE).r > (VALUE).i))
(1 row)

regression=# alter type complex drop attribute r;
ALTER TYPE
regression=# select pg_get_constraintdef((select max(oid) from pg_constraint));
pg_get_constraintdef
--------------------------------------------------------------
CHECK (((VALUE)."........pg.dropped.1........" > (VALUE).i))
(1 row)

Nothing seems to crash at this point, probably because we insert
nulls into dropped columns, so the CHECK just sees a NULL value
for "r" whenever it runs. But obviously, the next dump/reload
or pg_upgrade is not going to end well.

So what this shows is that we need a dependency on the particular
column named by the FieldSelect or FieldStore. Under normal
circumstances, that obviates the need for a dependency on the
FieldSelect's result type, which would match the column type.
I think concretely what we need is the attached.

(BTW, the getBaseType() is only necessary in HEAD, since before
domains-over-composites the argument of a FieldSelect couldn't
be a domain type.)

regards, tom lane