Update for newest Happy (GHC 7.8 compat)

I don't particularly know if this has any effect, but the newest version
of Happy seems to give this line the boot. Refer to
http://ro-che.info/articles/2014-03-08-happy-alex-ghc-7.8.html for more info.
Update to cereal 4

Build goes smoothly, tests pass.
Merge branch 'master' of https://github.com/gibiansky/IHaskell