Issue: ACK behavior with ordering and duplicate elimination

The spec should specify whether ACKs are sent before or after message
ordering, and before or after duplicate elimination. Currently the spec is
silent on this. 

Here is a proposal:

A WSRM receiver must send the ACK after duplicate elimination (in order to
not send duplicate ACKs).

A WSRM receiver should send the ACK before ordering (as opposed to when the
message is delivered to the app, since this will delay the ACK for all
messages queued up waiting for a delayed message in a sequence).

Comments?

Scott