Re: Fixing some ancient errors in hash join costing

I wrote:
> I was amused to notice that the postgres_fdw.out change made in my
> patch reverts one made in aa86129e1 (which also affected semijoin
> costing).  So we've had trouble before with that test case being
> fundamentally unstable.  I wonder if we shouldn't do something to try
> to stabilize it?  I see that the test immediately before this one
> forces the matter by turning off enable_sort (which'd affect only
> the local side not the remote).  That's a hack all right but maybe
> we should extend it to this test.

Here's a v2 patchset that splits that out as a separate change for
clarity's sake.  I also spent a bit of effort on commit log messages,
including researching the git history.

			regards, tom lane