Test that acknowledged duplicate changes update ghost bucket

[dmsnell]

In #73 and #74 we added tests to confirm that we stop sending changes after we hear from the server that they are duplicate changes. We stopped short, however, in testing of confirming that the acknowledged entity is updated in the ghost store to the version it should be.

Write a new test which upon acknowledge confirms that the local copy of the entity includes the change that was marked as a duplicate and that it's fully updated as it should be.