Ticket 256: add INSTEAD OF support for triggers

Hi,

It was much easier than I previously thought. This patch adds a Triggers
node in the each view object node if you're connected to a 9.1
PostgreSQL server. You can add and see triggers on views.

It's not ready to be commited. I still have a bug to fix. I tried since
two days, and I can't make it work. My issue is with the Triggers node.
I should have the "Create a new object..." button enabled in the toolbar
and a "New trigger" (or whatever it's labelled) item in the contextual
menu. But I don't have them. I really don't understand why. View objects
seem to be treated differently than others but, despite many tests, I
can't make it work.

You can still test the patch because you have the capacity to create a
trigger on a view with a contextual menu available on the view object node.

If someone has a pointer to help me fix this patch, I would really
appreciate it.

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