haddock: unset GHC_PACKAGE_PATH before checkPhase

https://github.com/NixOS/nixpkgs/issues/3721
Merge pull request #86 from Fuuzetsu/haddock

haddock: unset GHC_PACKAGE_PATH before checkPhase
cabal2nix.cabal: tentatively bump version number
Update post-process hook for ghc-mod.
Add post-process hook for hsyslog.