Separate &boolean type into &true and &false

Separate &boolean type into &true and &false

* module/language/cps/types.scm (&all-types): Represent true and false
  as separate bits, so that #f can be removed from types on true
  branches.  Adapt all users.

* module/language/cps/type-fold.scm (&scalar-types):
  (fold-and-reduce): Adapt to boolean type representation change.