update ajax() signature to match _ajax()
Merge pull request #257 from heartsentwined/ajax-signature

update ajax() signature to match _ajax()
Fix dirty tracking test to compare Dates.
Serialize attrs before comparing for dirty tracking.
Merge pull request #264 from karenliu1/karen/dirty-tracking-attrs

Karen/dirty tracking attrs
Merge branch 'master' of https://github.com/ebryn/ember-model