BUG #3424: Not able to drop trigger(RI_trigger*) on specific table.

The following bug has been logged online:

Bug reference: 3424
Logged by: S R Madhu
Email address: sraj_madhusr(at)yahoo(dot)com
PostgreSQL version: 8.0.3
Operating system: Linux RH6.2
Description: Not able to drop trigger(RI_trigger*) on specific table.
Details:

We have created a table "student".
Foreign key and triggers are created in student. We are able to map triggers
and constraints from pg_class table.

We have used following mapping mechanism to get the trigger name.
pg_class.relfilenode -> pg_trigger.tgrelid.

We have used following mapping mechanism to get the constraint name.
pg_class.relfilenode -> pg_constraint.conrelid.

Problem : After ALTER TABLE command to this table, We are not able to map
triggers/constraints and tables.
relfilenode in pg_class is changed after ALTER TABLE.
but this is not reflected in pg_constraint/pg_triggers.

Please do the needful.