Added todo to profile propParse's use of fvoid vs if statements

lib/util.js

@@ -171,6 +171,8 @@ exports.clone = function clone( data, deep )
  */
 exports.propParse = function( data, options )
 {
+    // todo: profile; function calls are more expensive than if statements, so
+    // it's probably a better idea not to use fvoid
     var fvoid          = function() {},
         callbackEach   = options.each          || undefined,
         callbackProp   = options.property      || fvoid,