[js] Emit a warning on stderr instead of stdout so it doesn't get mixed with normal output when running tests.

Author: pmurias

src/vm/js/nqp-runtime/core.js

@@ -313,7 +313,7 @@ op.newtype = function(how, repr) {
 op.can = function(obj, method) {
   if (typeof obj !== 'object' || obj instanceof NQPInt || obj instanceof CodeRef || obj instanceof Hash || obj instanceof NQPArray) return 0;
   if (!obj._STable.methodCache) {
-    console.log('we have no method cache, checking: ' + method);
+    console.warn('we have no method cache, checking: ' + method);
     return 0;
   }
   return obj._STable.methodCache.hasOwnProperty(method) ? 1 : 0;