Yep, looks like I needed to manually install dovecot-managesieved and dovecot-sieve, thanks.
It still broke everything though... it isn't a very smooth upgrade as I was led to believe, and I confess I don't know enough about what I'm doing to figure it out (yet). I might just back up my data, reset my whole setup, reinstall iredmail from scratch, and restore the data.
Thanks though!