hasMany update for Ember Data 1.0.0-beta.9

It seems `DS.RelationshipChange` is `undefined` in Ember Data 1.0.0-beta.9. As such `hasMany` relationships throws a `Cannot read property 'determineRelationshipType' of undefined`. Upon inspection of the source code of Ember Data 1.0.0-beta.9, the new code to be used is what has been added. I have confirmed this works.