Consistency error with R = 1

[vrv]

When the system is run with R=1 (no replicas), then there is a potential consistency bug (as verified by dBug: http://www.cs.cmu.edu/~jsimsa/dbug/ )

Specifically, when a node joins the system, it takes over for a range from another node. Get() requests during a particular time in this process must be served by an interim tail (the node before the old tail) of a chain. With R > 1, this interim tail exists, but when R=1, there is no interim tail. Therefore, these requests need to be buffered and sent later, or alternatively should return an error of the form "try again" so that the node join can complete fully.