Fix 4 clojure.core bugs surfaced by JVM certification

The corpus certifier (test/conformance) flagged four cases where jolt's
hand-written :expected matched a real defect rather than Clojure. Fixed in the
jolt-core overlay, corrected the spec :expected, re-certified against JVM Clojure:

- ex-message: returns nil for a non-throwable (dropped the lenient string branch);
  still returns the message for ex-info. (jolt-l8e8)
- munge: preserves the argument's type — a symbol munges to a symbol, not a string.
  (jolt-hc35)
- print: (print nil) emits "nil", not "" (top-level nil guard; str yields "").
  (jolt-pqio)
- bounded-count: uses the counted? fast path (full count), else counts up to n via
  seq — was (min n (count coll)), wrong for counted colls. Added an uncounted-coll
  spec case. (jolt-2507)

Removed the 4 :bug entries from known-divergences.edn (now certified), regenerated
corpus + profile, re-minted the Chez bootstrap seed (clojure.core changed). Gates:
Janet 155/0, JVM certify clean, both Chez corpus gates 2534 (floors raised),
bootstrap 6/6, fixpoint intact.

test/spec/exceptions-spec.janet

@@ -43,4 +43,4 @@
    "(try (try (throw (ex-info \"inner\" {})) (catch :default e (throw e))) (catch :default e (ex-message e)))"]
   ["ex-data on non-ex"    "nil"       "(ex-data 42)"]
   ["ex-cause on non-ex"   "nil"       "(ex-cause {:k 1})"]
-  ["ex-message of string" "\"hi\""    "(ex-message \"hi\")"])
+  ["ex-message of string" "nil"        "(ex-message \"hi\")"])