Zoltan: safe way to get the recursive bisection tree
Created by: egboman
Some applications need the tree corresponding to recursive bisection in partitioning methods like RCB and PHG. Currently they assume "natural" order, for example ((0,1), (2,3)) for k=4. This is actually not guaranteed to hold by Zoltan and in fact LB_REMAP could permute the parts and "mess things up". There should be a safer API for applications to use, both in Zoltan and Zoltan2.