Address Ember.ajax PR Issues

Addresses the following issues brought up in https://github.com/emberjs/ember.js/pull/4148:

* Label anonymous functions.
* Label promises.
* Only pass resolve or reject as needed.
* Throw an instance of Ember.Error (to allow future customizability).

This also updates the Ember version in `bower.json` to allow `>=1.2` and `<2` (it was previously locked to 1.2.x).