Fix seven more JVM divergences (rewrite-clj full suite)

Running the whole rewrite-clj test suite (159 tests) surfaced seven more bugs;
with these it passes 3377/0/0. Each is a general jolt/JVM divergence:

- *out* was pinned to the startup stdout port, so (.write *out* …) escaped a
  with-out-str capture (z/print writes via *out*). It now resolves the live
  current-output-port, like print/__write, so a redirect is seen.
- nth / assoc past the end of a vector or seq threw a bare Chez error (class
  :object). Throw IndexOutOfBoundsException, matching the JVM.
- A number's .toString(radix) ignored the base. Render in the base, lowercase
  (rewrite-clj rebuilds 0xff / 0377 / 2r1001 through it).
- A required namespace's own :as aliases leaked into its requirer: the loaded ns
  form compiles while (chez-current-ns) is still the requirer, so ce-scan-requires!
  registered the loaded ns's aliases under the wrong ns and clobbered a same-named
  alias there. Register an (ns NAME …) form's aliases under NAME.
- A quoted collection dropped its metadata; now it keeps USER metadata (drops the
  reader's :line/:column/:file), like a Clojure quoted constant.
- enumeration-seq only did (seq e); it now drives a java.util.Enumeration through
  hasMoreElements/nextElement, and StringTokenizer implements them.

Regressions: corpus rows (with-out-str/*out*, nth/assoc bounds, toString radix,
quote metadata, enumeration-seq) certified against JVM; a smoke fixture for the
alias leak (a required ns's alias must not leak). tools.reader + rewrite-clj added
to docs/libraries.md. make test green.

host/chez/seq.ss

@@ -152,9 +152,9 @@
                            (if (jolt-nil? s) last (loop (jolt-seq (seq-more s)) (seq-first s)))))
 ;; nth over a seq (walks; forces lazily). default? selects the 3-arg behavior.
 (define (seq-nth coll i default? d)
-  (if (fx<? i 0) (if default? d (error 'nth "index out of bounds"))
+  (if (fx<? i 0) (if default? d (jolt-throw (jolt-host-throwable "java.lang.IndexOutOfBoundsException" "index out of bounds")))
       (let loop ((s (jolt-seq coll)) (i i))
-        (cond ((jolt-nil? s) (if default? d (error 'nth "index out of bounds")))
+        (cond ((jolt-nil? s) (if default? d (jolt-throw (jolt-host-throwable "java.lang.IndexOutOfBoundsException" "index out of bounds"))))
               ((fx=? i 0) (seq-first s))
               (else (loop (jolt-seq (seq-more s)) (fx- i 1)))))))