ocaml: phase 4 integer division semantics + Int module + max_int/min_int (+5 tests, 525 total)

Three things in this commit:

1. Integer / is now truncate-toward-zero on ints, IEEE on floats. The
   eval-op handler for '/' checks (number? + (= (round x) x)) on both
   sides; if both integral, applies host floor/ceil based on sign;
   otherwise falls through to host '/'.

2. Fixes Int.rem, which was returning 0 because (a - b * (a / b))
   was using float division: 17 - 5 * 3.4 = 0.0. Now Int.rem 17 5 = 2.

3. Int module fleshed out:
   max_int / min_int / zero / one / minus_one,
   succ / pred / neg, add / sub / mul / div / rem,
   equal, compare.

Also adds globals: max_int, min_int, abs_float, float_of_int,
int_of_float (the latter two are identity in our dynamic runtime).

  17 / 5         = 3
  -17 / 5        = -3   (trunc toward zero)
  Int.rem 17 5   = 2
  Int.compare 5 3 = 1

lib/ocaml/eval.sx

@@ -418,7 +418,15 @@
       ((= op "+")    (+ lhs rhs))
       ((= op "-")    (- lhs rhs))
       ((= op "*")    (* lhs rhs))
-      ((= op "/")    (/ lhs rhs))
+      ((= op "/")
+        ;; OCaml's `/` is integer division on ints, float on floats.
+        ;; Pick floor on ints.
+        (cond
+          ((and (number? lhs) (number? rhs)
+                (= (round lhs) lhs) (= (round rhs) rhs))
+            (let ((q (/ lhs rhs)))
+              (if (>= q 0) (floor q) (ceil q))))
+          (else (/ lhs rhs))))
       ((= op "+.")   (+ lhs rhs))
       ((= op "-.")   (- lhs rhs))
       ((= op "*.")   (* lhs rhs))