Public make-cont-folder

Public make-cont-folder

* module/language/cps.scm (make-cont-folder): Add global? parameter, and
  make public.
  (fold-conts): Adapt.
  (fold-local-conts): Use make-cont-folder, and take a function instead
  of a continuation.

* module/language/cps/arities.scm (fix-clause-arities, fix-arities*):
* module/language/cps/compile-bytecode.scm (collect-conts):
* module/language/cps/elide-values.scm (elide-values*): Adapt to
  fold-local-conts change.