Make feasible tree explicit
Build explicit feasible tree
Network simplex algorithm for ranking
Checkpoint before trying Graphviz network simplex algorithm
Fixed bugs in cut value computation
Handle arbitrary fanout in spanning tree
Remove debugging statements
Start on assigning nodes to ranks
Merge branch 'master' of https://github.com/cpettitt/dagre into cpettitt-master

Conflicts:
	lib/rank.js
Bug fixes after merge
Use prefRank for ranking constraints
Remove simplex algorithm from master branch
Add tests.  Reverse edges to min and from max in acyclic
Merge pull request #90 from Concurix/master

Rank constraints