rt: Fix iaac_init using wrong type and not seeding correctly

This was a result of changing the vector representation to contain
a box header.

src/libcore/rand.rs

@@ -303,6 +303,17 @@ mod tests {
         assert ra.gen_str(100u) == rb.gen_str(100u);
     }
 
+    #[test]
+    fn rng_seeded_custom_seed2() {
+        let seed = [2u8, 32u8, 4u8, 32u8, 51u8];
+        let ra = rand::seeded_rng(seed);
+        // Regression test that isaac is actually using the above vector
+        let r = ra.next();
+        #error("%?", r);
+        assert r == 890007737u32 // on x86_64
+            || r == 2935188040u32; // on x86
+    }
+
     #[test]
     fn gen_int_range() {
         let r = rand::rng();

src/rt/rust_builtin.cpp

@@ -204,7 +204,7 @@ rand_new() {
 }
 
 extern "C" CDECL void *
-rand_new_seeded(rust_vec* seed) {
+rand_new_seeded(rust_vec_box* seed) {
     rust_task *task = rust_get_current_task();
     rust_sched_loop *thread = task->sched_loop;
     randctx *rctx = (randctx *) task->malloc(sizeof(randctx),

src/rt/rust_util.h

@@ -128,16 +128,16 @@ inline void isaac_seed(rust_kernel* kernel, uint8_t* dest)
 }
 
 inline void
-isaac_init(rust_kernel *kernel, randctx *rctx, rust_vec* user_seed)
+isaac_init(rust_kernel *kernel, randctx *rctx, rust_vec_box* user_seed)
 {
     memset(rctx, 0, sizeof(randctx));
 
     char *env_seed = kernel->env->rust_seed;
     if (user_seed != NULL) {
         // ignore bytes after the required length
-        size_t seed_len = user_seed->fill < sizeof(rctx->randrsl)
-            ? user_seed->fill : sizeof(rctx->randrsl);
-        memcpy(&rctx->randrsl, user_seed->data, seed_len);
+        size_t seed_len = user_seed->body.fill < sizeof(rctx->randrsl)
+            ? user_seed->body.fill : sizeof(rctx->randrsl);
+        memcpy(&rctx->randrsl, user_seed->body.data, seed_len);
     } else if (env_seed != NULL) {
         ub4 seed = (ub4) atoi(env_seed);
         for (size_t i = 0; i < RANDSIZ; i ++) {