Class should undef Module#prepend_features on own scope as Module#append_features

Is this intended?

ruby -v

* ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-linux]
* ruby 2.1.0dev (2013-08-09 trunk 42476) [x86_64-linux]

```ruby
Class.new.__send__ :append_features, Module.new #=> NoMethodError: undefined method `append_features' for #<Class:0x007f4473d178b0>
Class.new.__send__ :prepend_features, Module.new #=> TypeError: wrong argument type Class (expected Module)
```