Delayed cleanup ioref tests

[phadej]

Rebase of #622, with tests changed to use IORef

[phadej]

I'm ok with merging this, and then rewriting DelayedIO to use

newtype DelayedIO a = DelayedIO { runDelayedIO' :: ReaderT Request (ResourceT IO) (RouteResult a) }
-- or even
newtype DelayedIO a = DelayedIO { runDelayedIO' :: ReaderT Request (ResourceT (RouteResultT IO)) a }

opinions on this, @alpmestan, @jkarni?

---

for the reference: newtype ResourceT m a = ResourceT { unResourceT :: I.IORef ReleaseMap -> m a } from http://hackage.haskell.org/package/resourcet

[alpmestan]

There's some build failure to address (https://travis-ci.org/haskell-servant/servant/jobs/192826872#L393) -- for ghc 7.8. Other than that, LGTM. We can merge once it's fixed.

[jkarni]

Why not just use ResourceT (and remove CleanupRef) from the start? It seems like we're just mimicking ResourceTs functionality, which, given how subtle these things can be (e.g., what happens in the presence of forks), is probably going to bite us.

[phadej]

@jkarni I'll make a refactor PR today.