The new 'concurrency' package is starting at version 1.0.0.0 because the
API is already very mature (copied from base).
This breaks the dejafu-0.2 compatibility of async-dejafu.
Closes#51.
async-dejafu, hunit-dejafu, and tasty-dejafu only get a minor bump
because the API didn't change, only the dependencies. I'm not entirely
sure how to fit that properly into the PVP.