Make Specialise close over kind variables (fixes Trac #8196)
This is a lingering bug from the introduction of polymorphic kinds. In the specialiser we were specialising over a type, but failing to specialise over the kinds it mentions. The fix is simple: add a call to closeOverKinds. Most of the patch is to add closeOverKinds, and to use it in a few other places where we are doing essentially the same thing.