* The main change is to suppress printing (in types) of
     kind for-alls
     kind applications
  The new flag -fprint-explicit-kinds prints them as before
  (by analogy with the existing -fprint-explicit-foralls)

* I also took advantage of the fact that SDoc now has access
  to DynFlags, to tidy up the way in which explicit for-alls
  are printed.  Instead of passing a boolean flag around, we
  now simply consult the DynFlags.  Much neater.

I still need to add documentation for the flag