Example of severe speed regression in ember-data

As discussed [on the forum](http://discuss.emberjs.com/t/10-slowdown-in-store-pushpayload-with-ember-data-beta-11/6608), when I upgraded my app from Ember 1.7 and Ember Data beta 9 to Ember 1.8 and Ember Data beta 11 I noticed a large slowdown in the time taken to push records into the store.

This PR contains code which does what my app does. Apologies for the large number of models but I thought it was best to illustrate the relationships etc I have set up.

Running this code with  Ember 1.7 and Ember Data beta 9 takes a total of around 1.6 seconds on my laptop. Running it with Ember 1.8 and Ember Data beta 11 takes about 2.6 seconds - a 62% slowdown!

On my target platform of Android the code runs much slower and so the slow down is even more significant.

Hopefully this example code can help tracking down where things have slowed down!
You're right, that's a mistake / some old code. Removing the line the app still works (when I create `requiredItem`s I set `equipment: homeController.get('equipmentItems' + requiredType.get('id')),`) - I guess I could define the property as `DS.hasMany('equipment_item')` although this data is never sent over the wire (I add it to the model so that when the model is passed into a component the component has access to the equipment items that can be selected from)