_parseError should be an instance of Error.

Fixes a regression introduced by #319
while still providing a fix for #318.

lib/jison.js

@@ -1359,13 +1359,9 @@ function parseError (str, hash) {
     if (hash.recoverable) {
         this.trace(str);
     } else {
-        function _parseError (msg, hash) {
-            this.message = msg;
-            this.hash = hash;
-        }
-        _parseError.prototype = Error;
-
-        throw new _parseError(str, hash);
+        var error = new Error(str);
+        error.hash = hash;
+        throw error;
     }
 }