fs: added an argument check in fs.watchFile

Fixes #1324.

lib/fs.js

@@ -629,6 +629,10 @@ fs.watchFile = function(filename) {
     listener = arguments[1];
   }
 
+  if (!listener) {
+    throw new Error('watchFile requires a listener function');
+  }
+
   if (options.persistent === undefined) options.persistent = true;
   if (options.interval === undefined) options.interval = 0;