Re: Extended Statistics set/restore/clear functions.

>
> And here's a rebased set
>
> 0001 - adds a test left out of dependencies
> 0002 - mcv (plus pgdump)
> 0003 - exprs (plus pgdump)
> 0004 - capstone set-difference test that could not have succeeded until
> all stat kinds were implemented.
>

Before I forget, one thing that I did find notable is that the
mcv/expressions type importing code bypasses statatt_get_type() now, which
means that there is only one caller for this function, and it could be
moved back to being static.

Furthermore statatt_get_type() only exists because the two varietals of
examine_attribute() are just slightly off what we need - the one in
analyze.c will skip attributes with a target set to 0, and the one in
extended_stats.c only handles expressions. So there might be some
consolidation possible, but we'd have to change the code already being run
for regular ANALYZE and up til now that's been something I haven't wanted
to do.

>