Error when lock conflict on REPLACE function

Severity: Annoyance
Versions Tested: 8.4.2
Platform: Linux RHEL 5.4
Reproduceable: always
Steps to reproduce:

1. Create a function.
2. In one session, start an explicit transaction.
3. Do a CREATE OR REPLACE on the same function, but do not commit.
4. Open a 2nd session, and an explicit transaction in that session.
5. Do a CREATE OR REPLACE on the same function in the 2nd session.
6. COMMIT the 2nd session.
7. COMMIT the 1st session.
8. You get:

ERROR: duplicate key value violates unique constraint
"pg_proc_proname_args_nsp_index"
SQL state: 23505

What should have happened: the 2nd replace should have succeeded.  Or it
should have given a user-friendly error message.  Opinions?

--Josh Berkus