Replicated disorderly cart is broken

[neilconway]

There are errors in both the design and the implementation. Implementation:

1. @addy is used but never assigned to, as far as I can tell.
2. I haven't tracked down why, but writes aren't successfully making it from action_msg to mcast_send -- i.e., we aren't multicasting kvs ops when we see client requests
3. The destructive cart code assumes that the kvget_response for a given kvget will be delivered in the same timestep. When using a replicated KVS, this is not the case.

Design: more coordination needed. There is no reason to think that (a) client write order will be respected when writes are applied at KVS replicas (b) all writes will be applied when checkout is received.