Fix some lints

[AaronFriel]

These just make hlint and ghc-mod happier. There was a lint I did not change (redundant typeclass) which shows up on a -Wall.

[AaronFriel]

It appears the language pragma issue is this: https://github.com/ndmitchell/hlint/issues/125

{-# LANGUAGE
  OverloadedStrings,
  ScopedTypeVariables,
  TypeFamilies,
  DataKinds,
  FlexibleContexts
  #-}

Parsed fine.

[neongreen]

• I'm fine with changing pragmas style, it makes things easier if you use e.g. Emacs's automatic pragma insertion. I wanted to do it myself.

• I think I had some subtle and vague reasons for why when (not ...) was preferred to unless in some places, but I guess it does more harm than good.