make model redefinition a warning instead of an exception
make model redefinition a warning instead of an exception

spgarbet/pysb,spgarbet/pysb,johnbachman/pysb,pysb/pysb,alubbock/pysb-legacy,alubbock/pysb-legacy,neurord/pysb,LoLab-VU/pysb,d-fan/pysb,johnbachman/pysb,jmuhlich/pysb,neurord/pysb,alubbock/pysb-legacy,alubbock/pysb,d-fan/pysb,d-fan/pysb,LoLab-VU/pysb,alubbock/pysb-legacy,neurord/pysb,spgarbet/pysb