remerged ChooseBooleanStep and ChooseMapStep to ChooseStep with only one Strategy. Was actually easy when you convert the Boolean form to the Map form in the this(constructor). Removed all step methods from Traversal. We are no longer going to assume that Traversal has steps so that when people make their own DSLs, they are not forced to have count(), cap(), trackPaths(), etc. However, this causes problems for VertexPrograms (e.g. PageRank) that requires the Traversal have a count() method. To rectify this, I created a marker/ package where we now have CountTraversal interface with a count() method. Thus, PageRankVertexProgram requires a CountTraversal... just so happens GraphTraversal provides that.
merged master