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/runtime.sx

@@ -466,6 +466,21 @@
      let abs n = if n < 0 then 0 - n else n
      let max a b = if a > b then a else b
      let min a b = if a < b then a else b
+     let max_int = 4611686018427387903
+     let min_int = -4611686018427387904
+     let zero = 0
+     let one = 1
+     let minus_one = -1
+     let succ n = n + 1
+     let pred n = n - 1
+     let neg n = 0 - n
+     let add a b = a + b
+     let sub a b = a - b
+     let mul a b = a * b
+     let div a b = a / b
+     let rem a b = a - b * (a / b)
+     let equal a b = a = b
+     let compare a b = if a < b then -1 else if a > b then 1 else 0
    end ;;
 
    module Float = struct
@@ -832,6 +847,11 @@
    let string_of_float f = _string_of_float f
    let string_of_bool b = if b then \"true\" else \"false\"
    let int_of_string s = _int_of_string s
+   let max_int = 4611686018427387903
+   let min_int = -4611686018427387904
+   let abs_float f = if f < 0.0 then 0.0 -. f else f
+   let float_of_int n = n
+   let int_of_float f = f
    ")
 
 (define ocaml-stdlib-loaded false)