Ticket 118: Exclusion constraints

Hi,

At least, I finally did it :)

This patch adds support for exclusion constraint (9.0 new feature). All
examples from Magnus's talk (Beyond Unique) work with this patch.

Anyway, this patch needs more work:

1. Displayed in both Constraints and Indexes

I don't know why but each exclusion constraint is displayed two times.
In the indexes node (where it doesn't belong), and in the constraints
node (where it belongs). Any idea why? should not be too hard to find
out, but I'm unable to find it right now.

2. Need an icon

I copied the unique constraint icon, but we really need another one for
this specific constraint.

3. Probably some misunderstanding of the feature

Should we propose all operators for the columns? or just the ones
related to 1. the operator class 2. the column's type 3. something else?
actually, I propose all of them. But I don't think this is what we
should do.

In Magnus's talk, I see that only GiST is supported right now as an
index method. In PostgreSQL fine manual, it says that, to be usable, an
index should provide the amgettuple method. And I see three of them
support this method. Who's wrong? :)

Patch attached.

Comments welcomed :)


--
Guillaume
 http://www.postgresql.fr
 http://dalibo.com