patch review for Array ELEMENT Foreign Keys

The patch I reviewd is listed among CommitFest 2012-09 patches. I hope
it can be of some help, despite the fact, that I don't really feel like
being terribly qualified here.

Submission review
----
The patch goes cleanly against v9.3, as fetched by clonig current HEAD
from postgres git repository:

$ git clone ..
$ ./configure --with-readline
$ make
$ make world
$ make check

Apart from problems with substituted readline linkage, all that is this
patch related went smoothly.

The patch contains signifficant amount of testing code, so unit test it
provides gives confidence, that the patch works as intended.

Usability review
----
> Do we want that?
> Do we already have it?

As long as I'm concerned, this patch solves dataset partitioning
problem, which is hard to cope with otherwise. The nested storage this
patch provides solves the problem for me.

> Does the patch actually implement that?

Current version of the patch does not look like implementing "ON UPDATE
CASCADE" and "ON UPDATE DELETE", just yet; but this is documented....
Apart from that, basic FK functionality work fine.

Feature test
----

Before running "make check", I've made a few tests off the top of my
head, and everything was correct and intuitive.

"make check" also went flowlessly.

So the patch looks fine for me.

-R