handling multiple matching constraints in DetachPartitionFinalize()

Hi,
I was looking at the following code in DetachPartitionFinalize():

/* If there's a constraint associated with the index, detach it too
*/
constrOid =
get_relation_idx_constraint_oid(RelationGetRelid(partRel),
idxid);

As mentioned in email thread `parenting a PK constraint to a self-FK one`,
there may be multiple matching constraints, I think we should
call ConstraintSetParentConstraint() for each of them.

This means adding a helper method similar to
get_relation_idx_constraint_oid() which finds constraint and calls
ConstraintSetParentConstraint().

I am preparing a patch.
Please let me know if my proposal makes sense.

Thanks