General fixes shaken out by clojure/tools.reader

Running clojure.tools.reader's own suite on jolt surfaced a batch of general
gaps (all runtime, JVM-certified, no re-mint — reader.ss is loaded at runtime
and jolt-core has no octal literals, so selfhost holds):

Reader:
- (load "rel") resolves a non-/ path against the current namespace's directory,
  like Clojure — (load "common_tests") from clojure.tools.reader-test loads
  clojure/tools/common_tests.clj. Was resolved against the roots directly.
- Octal integer literals: 042 reads as 34, not decimal 42; octal string escapes
  (\377 is one char, not \0 + "00"). \oNNN char octal already worked.
- (symbol nil name) now equals (symbol name) and the reader literal — a nil
  namespace is the #f no-ns sentinel, not jolt-nil (jolt= compares ns by equal?).

clojure.test:
- thrown-with-msg? honors the class hierarchy (instance?) before falling back to
  a simple-name match, so (thrown-with-msg? RuntimeException ...) matches an
  ExceptionInfo, like thrown? already did.

Host interop (java layer):
- java.util.regex: Pattern.matcher / Matcher.matches / .group / .groupCount /
  .find, and Pattern/compile.
- clojure.lang: RT/map, PersistentList/create, PersistentHashSet/createWithCheck.
- java.lang.Character: digit / isDigit / isWhitespace / valueOf.
- java.util.LinkedList (Deque surface over the ArrayList backing); ArrayList /
  LinkedList are now seqable.
- BigInteger 2-arg ctor (string, radix) + .negate / .bitLength / .signum / .abs;
  BigInt/fromBigInteger and Numbers/reduceBigInt (identity on jolt's exact ints).

Suite: reader_test 22/30, reader-edn_test 13/16. The remaining failures are
fundamental numeric-model differences (no BigDecimal type; BigInt and Long are
one exact-integer type) or need JVM reflection (record/ctor tagged literals via
getConstructors) — out of scope.

make test green (+8 corpus rows, 0 new divergences), shakesmoke byte-identical.

host/chez/converters.ss

@@ -133,7 +133,12 @@
                         (else (loop (- i 1))))))))
          ((keyword? a) (jolt-symbol (keyword-t-ns a) (keyword-t-name a)))
          (else (error #f "symbol: requires string/symbol" a)))))
-    ((= (length args) 2) (jolt-symbol (car args) (cadr args)))
+    ;; (symbol ns name): a nil namespace is the no-ns sentinel #f (NOT jolt-nil),
+    ;; so (symbol nil "x") equals (symbol "x") and the reader literal 'x — jolt=
+    ;; compares ns with strict equal?, so a jolt-nil ns would differ from #f.
+    ((= (length args) 2)
+     (let ((ns (car args)))
+       (jolt-symbol (if (jolt-nil? ns) #f ns) (cadr args))))
     (else (error #f "symbol: wrong arity"))))
 
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