Backbone.sync success callback does NOT receive a model. The callback is called by jQuery.ajax, actually, and it received the 'data' (plain json object)
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Fix the Backbone.sync mock to return a JSON resp for Backbone 0.9.10

The altered spec emulates a backbone interal success callback such as inside fetch.
The backbone implementation of the arguments that are received by it vary by version.
Use the forBackboneCaller converter here so we can get consistent args.
Merge branch 'server-response'