OAK-585 - Reduce cost of commit retry
OAK-592 - MicroKernelIT conflictingMove and confilictingAddDelete tests fail on MongoMK 

-Implemented improvements to CommitCommand outlined in OAK-585
-Fixed OAK-592 by adding basic conflict detection in mergeNodes

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1440417 13f79535-47bb-0310-9956-ffa450edef68