Changes prior factor(s) in all populations

def change_prior(self,**kwargs):
        """Changes prior factor(s) in all populations
        """
        for kw,val in kwargs.items():
            if kw=='area':
                logging.warning('cannot change area in this way--use change_maxrad instead')
                continue
            for pop in self.poplist:
                k = {kw:val}
                pop.change_prior(**k)