Model creation and modification race condition

[headlessme]

If a model is modified several times in quick succession, before a response from the server is received this leads to duplicate models created in the local storage. This seems to be because the Backbone generated cid is ignored and instead a copy of the model is created in modelUpdatedWithResponse along with it's own GUID that's used in local storage.

What is the purpose of creating a copy of the model when an existing one is available and could be updated instead?

[nilbus]

Although we no longer use clone() because of #75, the commit message on e4f1ba8 explains the rationale behind not passing the original model to localsync.

Given this incorrect behavior you're seeing, maybe there is a better approach. I would consider any alternatives you come up with.