title: in ember-data, when in the lifecycle is a newly created record's id available?
body: <p>using the RESTAdapter in ember-data.  i create a record on the server, and i need to get the id of the newly created record.  that id gets passed back from the server, i can see it in the json returned.</p>
  
  <p>however, in the DS.Model's didCreate() callback, this.get('id') is undefined.</p>
  
  <p>i also tried adding a record.one('didCreate',aClass,aClass.onDidCreate) and checking newRecord.get('id') but it's also undefined.</p>
  
  <p>the didCommit callback doesn't seem to get called after createRecord() , so i'm not sure where else i should be checking in the lifecycle callbacks.  anyone know?</p>