stopgap fix for pathmerge problem introduced by #51 in commit 447146c
use null for default values in all pregelix messages
fix BubbleMerge bug where an incorrect major/minor to bubble dir was used
explicitly set the length to 0 at the beginning of BFS
fix scaffolding bug where incomingMsg details weren't included
use <enum>.values() instead of EnumSet.allOf()
Node uses null values and writes less to stream