decorators and mixins pass the class they are changing

So you can do cool things like...
```javascript
var MyClass = Fiber.extend(function(base) {
  return {
    reallyCoolMethod: function() { /* cool stuff */ }
  };
});

var MyDecorator = function(base) {
  return {
    reallyCoolMethod: function() {
      // more betterer cool stuff
      base.reallyCoolMethod.apply(this, arguments); // or preferably - base.reallyCoolMethod()
    }
  };
}
```