Reduce code size of division operators

Reduce code size of division operators

* libguile/numbers.c (scm_quotient): Reimplement in terms of
  scm_truncate_quotient.

  (scm_remainder): Reimplement in terms of scm_truncate_remainder.

  (scm_modulo): Reimplement in terms of scm_floor_remainder.

  (scm_euclidean_quotient, scm_euclidean_remainder,
  scm_euclidean_divide): Reimplement in terms of floor and ceiling.
  Make them non-extensible, because there is no need; they will work
  with any objects that implement the floor and ceiling division
  operators, and that can be tested using `negative?'.