Invoke Callbacks when model with temp id is destroyed

When a model with a temp id is destroyed, then the success and error
callbacks should be invoked too.
Model with temp id should not be marked as destroyed

If a model with a temp id is destroyed, it should not be marked as
destroyed. Because it has never been synced with the server.
Use hasTempId instead of knowing what a tempId is
Merge branch 'destroy-tempid'

Closes #115
Update changelog for #115
Merge branch 'master' into mocha
Convert the spec from #115 to an acceptance style spec
Test mode overrides
Remove an unused deferred
Test offline status code override
Test Backbone.DualStorage.offlineStatusCodes as a method returning a success code

This failing spec reveals a bug that will be fixed in the next commit.
Allow Backbone.DualStorage.offlineStatusCodes to include 200 OK as an offline status

- Rename error callback parameter to xhr, since that is really what it is
- Update the mock ajax callback xhr argument to always include the http status and response