Attempt to fix inheritance limitations: unique and foreign keyconstraints

Hi pg-hackers,

I'm trying to fix some of limitations in table inheritance. My first use case concerns "referencing" foreign keys in parent table.

The attached patch propagates foreign keys to inherited tables. I'm automatically cloning foreign keys from parent table into children (with right dependencies). It's the native implementation of work-around described in documentation section 5.9.1. (Caveats).

To be honest it's my first pg hack. Thus it might contain (serious) issues (please be lenient with it).
Furthermore it's not yet documented (TODO !!)

As far as I tested it works pretty well; the internal triggers are installed on CREATE TABLE .. INHERIT and even after ALTER TABLE .. INHERIT.

If you have few minutes to challenge this hack and give your advices, be my guest !

Kind regards,