Don't delete reference to cID when changing ID of a new record

Was running into record not found errors when trying to refer to a new AJAX record by its cID after it had successfully been created server-side. Since ID is set equal to cID initially on new records, `changeID()` ends up deleting the cID reference, such that you can no longer find the record by cID. This seems to have been a problem ever since IDs and cIDs were combined into `irecords`.

Let me know if this fix looks right.

PS: While debugging this, I wonder if `isNew()` is also broken because of the `irecords` combination. We're storing both ID and cID in `irecords`, and brand new objects get their IDs set to their cIDs, so wouldn't `isNew()` always return `false` now?