Please use this patch instead of my previously submitted one.
It is just remerged against HEAD for new alter_table.out stuff.
Another reason this patch is useful for _interactive_ users: imagine a
view based on a many way join. Imagine creating a complicated insert rule
that inserts into all the joined tables and when you insert you get a
check failure, but you need to know which actual table the constraint was
on that failed!
Chris
