Arboricx bundle format 1.1

We don't need SHA verification or Merkle dags in our transport bundle. Content
stores can handle both bundle and term verification and hashing.

lib/list.tri

@@ -68,3 +68,15 @@ any? = y (self pred : matchList
   (h z : or? (pred h) (self pred z)))
 
 intersect = xs ys : filter (x : lExist? x ys) xs
+
+nth_ = y (self n xs i :
+  matchList
+    t
+    (h r :
+      matchBool
+        h
+        (self n r (succ i))
+        (equal? i n))
+    xs)
+
+nth = n xs : nth_ n xs 0