Collection.add should accept a single model
Check that model exists before trying to verify uniqueness
Copy models array so someone can do coll.remove(coll.models)....
We should keep the same collection model when cloning
Apparently at should accept negative values
If this.routes = this.routes was doing something special, sorry
Don't add null/undefined ids to the modelMap
Don't modify options reference when passed to reset
previousAttributes should include the original attributes