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/java/host-static.ss

@@ -117,7 +117,12 @@
     ((string=? method "longValue") (->num (jnum->exact n)))
     ((string=? method "doubleValue") (->num n))
     ((string=? method "floatValue") (->num n))
-    ((string=? method "toString") (jolt-num->string n))
+    ;; .toString(radix) — BigInteger/Integer render in a base, lowercase like the
+    ;; JVM (rewrite-clj's integer node reconstructs 0xff / 0377 / 2r1001 this way).
+    ((string=? method "toString")
+     (if (pair? args)
+         (string-downcase (number->string (jnum->exact n) (jnum->exact (car args))))
+         (jolt-num->string n)))
     ((string=? method "hashCode") (->num (jnum->exact n)))
     ;; Double/Float .isNaN / .isInfinite (a non-flonum is neither).
     ((string=? method "isNaN") (and (flonum? n) (not (= n n))))