Re: POC: converting Lists into arrays

I wrote:
>> * Rationalize places that are using combinations of list_copy and
>> list_concat, probably by inventing an additional list-concatenation
>> primitive that modifies neither input.

> I poked around to see what we have in this department. There seem to
> be several identifiable use-cases:
> [ ... analysis ... ]

Here's a proposed patch based on that. I added list_concat_copy()
and then simplified callers as appropriate.

It turns out there are a *lot* of places where list_concat() callers
are now leaking the second input list (where before they just leaked
that list's header). So I've got mixed emotions about the choice not
to add a variant function that list_free's the second input. On the
other hand, the leakage probably amounts to nothing significant in
all or nearly all of these places, and I'm concerned about the
readability/understandability loss of having an extra version of
list_concat. Anybody have an opinion about that?

Other than that point, I think this is pretty much good to go.

regards, tom lane