changed communicator message tracking to use sets for speedy membership lookups
changed communicator message tracking to use sets for speedy membership lookups

rwcarlsen/cyclus,hodger/cyclus,Baaaaam/cyclus,hodger/cyclus,mbmcgarry/cyclus,hodger/cyclus,mbmcgarry/cyclus,gidden/cyclus,gidden/cyclus,Baaaaam/cyclus,Baaaaam/cyclus,hodger/cyclus,hodger/cyclus,rwcarlsen/cyclus,rwcarlsen/cyclus,mbmcgarry/cyclus,gidden/cyclus,gidden/cyclus,mbmcgarry/cyclus,rwcarlsen/cyclus