ENG-4314 Support JSON predicates in EE multiCOW.
ENG-4314 Review feedback - get rid of StreamPredicate class.
ENG-4314 CopyOnWriteTest now uses json_spirit, as per review comments.
ENG-4314 Add json_spirit_writer to fix EE build.
Merge pull request #429 from VoltDB/ENG-4314

ENG-4314 Support JSON predicates in EE multiCOW.