contrib/rtree_gist into core system?

I've mentioned this a couple times now, but here is an official
proposal:

I would like to move the contrib/rtree_gist functionality into the core
system before feature freeze. There are a couple arguments in favor:

* It's way past time GiST indexes got some regression testing in the
core build. rtree_gist is the only very plausible candidate for
near-term integration: I don't think tsearch2 is ready for that, and
the other GiST-using contrib modules are not of sufficient general
usefulness.

* With the recent WAL-ization and hoped-for concurrency fixes, GiST
is definitely superior to R-tree for practical use. I don't see the
percentage in continuing to maintain the R-tree code indefinitely.
By integrating the opclasses needed to replace R-tree, we can start
down the path to deprecating and eventually removing R-tree.

Any objections?

regards, tom lane