Shells should send console.warn and error to stderr

Right now they go to stdout, which makes running with json-dumping less
effective since we `warn` the subset of tests being run.

Author: kmiller68

shell-config.js

@@ -29,8 +29,8 @@ if (typeof console == "undefined")
 
 console.debug ??= (...args) => console.log("Debug:", ...args);
 console.log ??= (...args) => print(args.join(" "));
-console.warn ??= (...args) => console.log("Warn:", ...args);
-console.error ??= (...args) => console.log("Error:", ...args); 
+console.warn ??= (...args) => printErr("Warn: " + args.join(" "));
+console.error ??= (...args) => printErr("Error: " + args.join(" "));
 console.assert ??=  (condition, message) => {
     if (!condition)
         throw new Error(`Assertion failed: ${message}`);