Support for constraint trigger (8.2 feature)

Hi,

Here is a patch that adds support for the constraint trigger, a feature
available since 8.2.

This patch adds a Constraint checkbox and the deferrable and deferred
checkboxes. Note that the "FROM referenced_table_name" clause is not
implemented as it "is not recommended for general use" according to the
manual.

I'm not sure the design is really good as I had to increase the dialog's
height quite a lot. It would probably be a good idea to add a new tab
and push some controls over there.

Comments?


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