recreating table and foreign keys

Hi
I use Postgresql 7.2.2.
Sometimes I have to remove a column from my tables (psql):
1. alter table master_table rename to x;
2. \i tables.sql
3. insert into master_table select f1,f2,... from x
4. drop table x

I think, foreign keys referring from detail_table(s) to master_table 
have gone.
How to recreate foreign keys? I want to keep my database in better 
integrity, than now...

Tomasz Myrta