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.
Make relationshipType backwards compatible
Merge pull request #99 from ewalti/patch-1

hasMany update for Ember Data 1.0.0-beta.9