jolt's catch is (catch class binding body*); the binding (3rd element) must be
a symbol. Neither the analyzer nor the interpreter validated it, so a non-symbol
binding crashed with an internal Janet error (expected integer key for array...)
and, in the interpreter, a malformed clause whose body never threw was silently
swallowed (returned the try value). Clojure rejects a non-class/non-symbol catch
clause; match that with an up-front error in analyze-try and eval-try.
Surfaced building the Chez try/throw emit. Regression rows in exceptions-spec
(runs x3 modes) plus a unit test asserting the clean message in interpret and
compile. jolt-kg6p.
