Deprecate former underscored names.

This adds `DS.ContainerProxy` that is used to create factories that when instantiated lookup another. When the old names are looked up a deprecation is thrown indicating which container key was used for lookup and which should have been used.

Update `ember-dev` to latest version with recent changes adding an `expectDeprecation` helper (added [here](https://github.com/emberjs/ember-dev/pull/121)).

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Example `ContainerProxy` usage:

```javascript
var proxy = new DS.ContainerProxy(container);
proxy.registerDeprecations([
  {deprecated: 'serializer:_default',  valid: 'serializer:default'},
  {deprecated: 'serializer:_rest',     valid: 'serializer:rest'},
  {deprecated: 'adapter:_rest',        valid: 'adapter:rest'}
]);
```