UNICAST2: first-message-lost problem

If A sends its first message A#1 to B, but the network drops A#1, B won't be able to receive A#1 unless A sends another message.
Even the stable task won't help: as B only sends stable messages to connected members (and A isn't), it will never send a stable message to A.

SOLUTION:

• Use acking for the first message
• Continue sending the first message until it has been acked, or a configurable time period has elapsed
• Note that we cannot cancel this task based on membership (view changes), as unicast messages can be sent to members outside of our view