Add support for Backbone 0.9.10+

@MarrLiss,

In order to work with Backbone 0.9.10+, Backbone.sync implementations need to send `model, resp, options` instead of `resp, status, xhr` to the `success()` and `error()` callbacks. This change was not documented in the Backbone changelog (I might see if I can add it), but it is visible in the [Backbone 0.9.10 Diff](https://github.com/documentcloud/backbone/compare/0.9.9...0.9.10) (just search for "success" or "error" in the "Files Changed" tab).

This pull request supports the new callback style while maintaining backward compatibility with the old style if `Backbone.VERSION` is less than 0.9.10.

Note that if you merge #6, the new call to `success()` inside `successFind()` will need similar treatment. Let me know if you merge it, so I can update this pull request to take care of that.