fix uncaught error throwing.

lib/events.js

@@ -77,8 +77,7 @@ EventEmitter.prototype._emit = function(type, args) {
 
   if (!handler) {
     if (type === 'error') {
-      throw new Error('Unhandled error event: '
-        + JSON.stringify(slice.call(arguments)));
+      throw new args[0];
     }
     return;
   }