Apply autoincremented keypaths when adding

If I understand IndexedDB correctly, then an object being added to a store that has a keypath and is autoincremented should always have a property matching the keypath. So if I have a store with settings:

{autoincremented: true, keyPath: 'id'}

and I add an object:

{foo: 'bar'}

then I'd expect to get this back:

{foo: 'bar', id: 1}

Not sure about my solution but the tests are passing.