store_from_source(r, RedisStoreWithNumericLists) raises AttributeError ('store') #10

Found in the review of #9: store_from_source builds a store with object.__new__, which does not work for classes wrapped by wrap_kvs (they expect a .store attribute). Fix: have store_from_source construct wrapped classes properly, or document/raise a clear error. Repro: store_from_source(FakeRedis(), RedisStoreWithNumericLists)['k'].