Re: Window-functions patch handling of aggregates

> 1. Go back to Hitoshi's plan of passing WindowAggState to the
> aggregates.  This will require changing every one of the ten aggregates
> in the core distro, as well as every third-party aggregate that has
> a similar optimization; and we just have to keep our fingers crossed
> that anyone who's taking a short-cut will fix their code before it
> fails in the field.

Unfortunately, if we don't want to add an explicit iswindowable flag
(and I understand that that's ugly), then I think this is the way to
go.  It's a shame that people will have to make code changes, but
inventing a fake AggState object just to get around this problem
sounds worse.  The array_agg code is new and the fact that it doesn't
follow the design pattern should be considered a bug in that code
rather than a justification for an ugly workaround.

...Robert