Re: eval_const_expresisions and ScalarArrayOpExpr

I wrote:
> Looking at the patch, it still seems solid, but I remember that one
> thing I was concerned about was whether the more generalized code
> was any slower.  Not sure about a good test case to measure that
> though --- const-simplification isn't a large chunk of most workloads.

This patch no longer applies cleanly on HEAD, so here's a rebased version
(no substantive changes).  As before, I think the most useful review task
would be to quantify whether it makes planning noticeably slower.

			regards, tom lane