This ensures that all object seeds are the same as for the corresponding reference Nengo model. It also ensures that seeds for all objects are set and the same whether precompute is True or False.
Depends on nengo/nengo#1476.
Computing the seeds before building, as I'm doing here, is something we've talked about adding to Nengo for a while. I would be open/happy to take the functionality here and move it to Nengo instead, since I think that is ultimately where we want it.