This is NOT the official source repository for OUnit, which you can find on ocamlcore darcs here. Instead, it's a git mirror of that repository, maintained using darcs-to-git.
Here's the procedure to pull patches from the upstream darcs repo:
git checkout upstream
curl https://raw.github.com/purcell/darcs-to-git/master/darcs-to-git > /tmp/darcs-to-git.rb
ruby -- /tmp/darcs-to-git.rb http://darcs.ocamlcore.org/repos/ounit
git checkout master
git merge upstream```