Yum upgrade of PostgreSQL 8.4 from to rc1 rendered data unusable

Dear PostgreSQL admins and gurus,

I always knew that installing Postgres using Yum/RPM/etc is a very bad
idea, but decided to try it on one my boxes that runs local wiki/Trac.

I added /etc/yum.repos.d/pgdg-84-centos.repo to my yum configuration
and installed PostgreSQL version 8.4devel_20090310-1PGDG.rhel5.i386

Today I ran "yum update", which quietly upgraded my installation to
"8.4rc1-1PGDG.rhel5.i386" and now my server does not start.

-bash-3.2$ pg_ctl --version
pg_ctl (PostgreSQL) 8.4rc1
-bash-3.2$ pg_ctl -D /db/data start
server starting
-bash-3.2$ FATAL:  database files are incompatible with server
DETAIL:  The database cluster was initialized with CATALOG_VERSION_NO
200902242, but the server was compiled with CATALOG_VERSION_NO
200904091.
HINT:  It looks like you need to initdb.

I do NOT have a pg_dump of the database because I did not anticipate
this idiocy.

I am looking for any help on how I can revert back to the previous
version of PostgreSQL so that I can read the database, do pg_dump, and
never EVER use yum again to upgrade it.

Please halp!

Konstantin