Some of the kind-checking and type-checking modules have become unruly.

Simon and I propose the new structure:

• KcTyClsDecls will handle kind-checking and generalization of datatype declarations. (That is, kcTyClGroup and children, including related functions in TcHsType)

• TcInstBinds will handle tcInstDecls2 and children

• TcTyConValidity will handle checkValidTyCon and children

• Fold the rest of TcInstDecls (essentially, tcInstDecls1) into what's left of TcTyClsDecls. TcInstDecls is removed.