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.

host/chez/build.ss

@@ -27,9 +27,12 @@
       (let ((l (get-line in)))
         (if (eof-object? l)
             (begin (close-port in)
-                   (let ((s (apply string-append (reverse acc))))
-                     ;; trim a trailing newline-equivalent (we joined without them)
-                     s))
+                   ;; rejoin with newlines (get-line stripped them). Callers use
+                   ;; single-line output; this just avoids silently concatenating
+                   ;; two lines into one corrupt token if a command emits more.
+                   (let ((ls (reverse acc)))
+                     (if (null? ls) ""
+                         (fold-left (lambda (s x) (string-append s "\n" x)) (car ls) (cdr ls)))))
             (loop (cons l acc)))))))
 
 (define (bld-system cmd)