[Yum] preupgrade locked up, we rebooted, ran preupgrade again and it succeeded but many dup pkgs now in rpmdb

[Gerry Reno]

We ran preupgrade (F9=>F10) on one machine and it locked up about 80% 
through the anaconda package install.  So we rebooted the machine and it 
came back up, we logged in and ran preupgrade again and this time it 
succeeded.  But now we notice there are a huge number of packages in the 
rpmdb from the old release.  How can we clear these out of this machine?

Regards,
Gerry