Failing test: merge should trigger appropriate change events

A slight tweak to the test you added in https://github.com/PaulUithol/Backbone-relational/commit/77eb89d9da345061d06aef87154328a867d536f1 shows a failing behavior.

Just like the original bug, this test passes if you change `reset` to `set`, though I don't see why it shouldn't work fine in either case.