ocaml: phase 5.1 safe_div.ml baseline + Result.equal/compare/iter_error (+3 tests, 592 total)

safe_div.ml: integer division returning Result. Sum-safe folds pairs,
skipping the Error branches.

  [(10,2); (20,4); (30,0); (50,5)]   ->  5 + 5 + 0 + 10 = 20

Result module additions (mirroring real OCaml's signatures):

  equal eq_ok eq_err a b
  compare cmp_ok cmp_err a b      Ok < Error (i.e. Ok x compared to
                                  Error e returns -1)
  iter_error f r

  Result.equal (=) (=) (Ok 1) (Ok 1)              = true
  Result.compare compare compare (Ok 5) (Ok 3)    = 1
  Result.compare compare compare (Ok 1) (Error _) = -1

30 baseline programs total.

lib/ocaml/runtime.sx

@@ -410,6 +410,25 @@
        match r with
        | Ok x -> ok_f x
        | Error e -> err_f e
+
+     let equal eq_ok eq_err a b =
+       match a with
+       | Ok x ->
+         (match b with Ok y -> eq_ok x y | Error _ -> false)
+       | Error e ->
+         (match b with Ok _ -> false | Error e2 -> eq_err e e2)
+
+     let compare cmp_ok cmp_err a b =
+       match a with
+       | Ok x ->
+         (match b with Ok y -> cmp_ok x y | Error _ -> -1)
+       | Error e ->
+         (match b with Ok _ -> 1 | Error e2 -> cmp_err e e2)
+
+     let iter_error f r =
+       match r with
+       | Ok _ -> ()
+       | Error e -> f e
    end ;;
 
    module String = struct