swarm class aggregator function bug

[tbrown122387]

The swarm class (without covariates) has the same bug that the other swarm class has (with covariates). Its aggregator functions it passes to the thread pool were off. Mirror the fix I made for the latter (See 28526af)

[tbrown122387]

fix is made, but tests are not in place. probably need a new test file with a model thrown in there