ocaml: phase 6 List.sort_uniq + List.find_map (+2 tests, 503 total)

sort_uniq:
  Sort with the user comparator, then walk the sorted list dropping
  any element equal to its predecessor. Output is sorted and unique.

  List.sort_uniq compare [3;1;2;1;3;2;4]  =  [1;2;3;4]

find_map:
  Walk until the user fn returns Some v; return that. If all None,
  return None.

  List.find_map (fun x -> if x > 5 then Some (x * 2) else None)
                [1;2;3;6;7]
  = Some 12

Both defined in OCaml syntax in runtime.sx — no host primitive
needed since they're pure list traversals over existing operations.

lib/ocaml/runtime.sx

@@ -158,6 +158,26 @@
 
      let stable_sort = sort
 
+     let rec sort_uniq cmp xs =
+       let sorted = sort cmp xs in
+       let rec dedup ys =
+         match ys with
+         | [] -> []
+         | [x] -> [x]
+         | a :: b :: rest ->
+           if cmp a b = 0 then dedup (b :: rest)
+           else a :: dedup (b :: rest)
+       in
+       dedup sorted
+
+     let rec find_map f xs =
+       match xs with
+       | [] -> None
+       | h :: t ->
+         match f h with
+         | Some v -> Some v
+         | None -> find_map f t
+
      let rec combine xs ys =
        match xs with
        | [] -> (match ys with