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
Merge pull request #56 from uci-cbcl/wbiesing/pregelix-messages-have-null-values

In pregelix messages, use null values to indicate usage