Trac error: Unsupported version control system "darcs"

I got this error after an OS upgrade:

Unsupported version control system "darcs": Can't find an appropriate component, maybe the corresponding plugin was not enabled?

To solve it I grabbed the latest darcs trac plugin:

darcs get http://darcs.arstecnica.it/trac-darcs

and installed it:

sudo python setup.py install

I then had to upgrade and resync each repository:

trac-admin /var/lib/trac/myrepo/ upgrade
trac-admin /var/lib/trac/myrepo/ resync