This patch, which fixes Trac #14566, makes LiberateCase a little
more conservative.  In particular:

* In libCaseBind, treat a recursive group as a whole, rather than
  binding-by-binding, allowing the group to be duplicated only if
    - the bindings /considered together/ are smaller than the
      liberate-case threshold (which is large by default)
    - none of them are thunks
    - none of them are guaranteed-diverging

  The latter condidtion is new, and happens to apply in the
  case of Data/Typeable/Internal.mkTrApp