[Moo] Track Class Instances with a Mutator

[Devign]

Hi guys

I wrote a Class Mutator to preserve class instances in an array, to
have the ability to alter all of them or just for debugging (console
etc.)
http://devign.me/mootools-track-class-instances-with-the-trackinstances-mutator/

For example:

var x=new MyClass();
var y=new MyClass();

MyClass.instances // [x, y]
MyClass.instances.each(function (o) { o.reposition(); });