Test case for cid order when adding model hashes

`Collection#add` in 0.9.9 inserts object hashes in reverse. This has the unintended consequence of creating `cid`s on the vivified models in reverse order as well, which broke code that relies on the `cid` as the marker for model insertion order. This behavior is reversed back to 0.9.2 behavior on `master`. This test case aims to ensure this behavior persists.