New test for rCM
Fixed empty.rke(). Used to create an empty RKE object that was not valid (could not pass the CHECK_rke() test)
Minor
 Fixed rke.empty() function
Added a more general test for matching and rke.cycles. This creates a graph with N triangles and (N-1) 2-way exchanges in a chain. It is easy to derive expression for max-matching for these graphs. See get.RKE0() function