Right ... I should've been more clear -- it's part of Carp. Reinstall Carp so you get Carp::Heavy. (which is of course, part of the main perl distribution, so this can get messy). As it's pure perl, you should be able to just extract Carp.pm and Carp/Heavy.pm from the distribution, and place them in the right place.

(there might be some easy way to install Carp from CPAN, without needing to pull down the whole perl-5.8.6 tarball, but I have no idea how ... but maybe someone else on here does)