Note the breaking bugfix for _super

#### Ever-present \_super (Breaking Bugfix)

Prior versions of Ember.js used a super mechanism that was un-safe for mixins. If more than one `_super` was called for a given function name and there was no terminating function, an infinite loop would occur. See [#3523](https://github.com/emberjs/ember.js/issues/3523) for further discussion.

The solution released in 1.5 fixes this behavior (see [#3683](https://github.com/emberjs/ember.js/pull/3683)), but also breaks the edge-case of using `_super` out of line. For instance:

```JavaScript
  doIt: function(){
    Ember.run.once(this, this._super);
  }
```

Is no longer a supported use of `_super`. See [this jsbin](http://emberjs.jsbin.com/xuroy/1/edit?html,js,output) for a live example. If this change impacts you, please comment on [#4632](https://github.com/emberjs/ember.js/pull/4301).