JVM-semantics fixes and small cleanups

- take-last / drop-last return seqs, not vectors: take-last wraps in seq; drop-last
  is the JVM (map (fn [x _] x) coll (drop n coll)) form (lazy, () when empty).
- cycle is lazy ((lazy-seq (concat coll (cycle coll)))) so it no longer counts its
  argument and terminates on a lazy/infinite input.
- fold's foldable-call catch uses :default, matching the rest of jolt-core and
  also catching a raw host condition from a folding primitive.
- alts! rejects non-channel ports with a clear error (put specs / :default are
  unsupported) instead of crashing inside ac-poll!.
- Misc: drop the unreachable second getCause clause; jolt-nth on a string raises
  'nth "index out of bounds" like the vector branch; name the inline fixpoint cap;
  bld-sh-capture rejoins lines with newlines; clarify a couple of comments.

jolt-core/clojure/core/20-coll.clj

@@ -188,13 +188,15 @@
 
 (defn replicate [n x] (map (fn [_] x) (range n)))
 
+;; Returns a seq (JVM does), nil when n<=0 or coll is empty.
 (defn take-last [n coll]
   (let [c (vec coll) len (count c)]
-    (when (pos? len) (subvec c (max 0 (- len n))))))
+    (when (pos? len) (seq (subvec c (max 0 (- len n)))))))
 
+;; The JVM definition: a lazy seq (() when empty), not a vector.
 (defn drop-last
   ([coll] (drop-last 1 coll))
-  ([n coll] (let [c (vec coll)] (subvec c 0 (max 0 (- (count c) n))))))
+  ([n coll] (map (fn [x _] x) coll (drop n coll))))
 
 (defn distinct?
   ([x] true)

jolt-core/clojure/core/40-lazy.clj

@@ -76,13 +76,11 @@
      (mapi 0 coll))))
 
 ;; --- cycle ---
+;; Lazy, like the JVM: never counts coll, so it terminates on a lazy/infinite
+;; argument instead of forcing it.
 (defn cycle [coll]
-  (if-let [vals (seq coll)]
-    (let [n (count vals)]
-      (letfn [(cstep [i]
-                (lazy-seq
-                  (cons (nth vals (mod i n)) (cstep (inc i)))))]
-        (cstep 0)))
+  (if (seq coll)
+    (lazy-seq (concat coll (cycle coll)))
     ()))
 
 ;; --- repeatedly --- ((f) throws on a non-fn; (take n …) throws on a non-number