Add mintree.ml, which allows us to keep track of the minimum-height tree that can be built from a forest of binary trees.
Add mintree.ml, which allows us to keep track of the minimum-height
tree that can be built from a forest of binary trees.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome