Darcs does export most of its module tree, but there's a problem: Darcs
relies on the current directory. It changes the current directory of the
process to the repo, and then proceeds using paths relative to the repo
dir. This is bad for my case here. If some other thread uses a relative
path (e.g. currently any repo path is relative by default) in parallel,
it will fail.
For now, the quick path around this problem is to use the `darcs`
program.
