Print infix type constructors in back-ticks

Fixes Trac #7609
Remove unused argument
Comments only
The type/kind variables of a class decl scope over the associated types

Fixes Trac #7601
Merge branch 'master' of darcs.haskell.org:/home/darcs/ghc
When quantifying associated types, we may have TyVars involved, not just TcTyVars
This required a little adjustment in zonkQuantifiedTyVars
Merge branch 'master' of darcs.haskell.org:/home/darcs/ghc
Merge branch 'master' of darcs.haskell.org:/home/darcs/ghc
Merge branch 'master' of darcs.haskell.org:/home/darcs/ghc