Break loop in new_sample_size

[spertus]

The while loop in new_sample_size needs to break at some point. Obvious choice is to break when the population size is reached; this is certainly true when sampling w/o replacement. If population size is reached without confirming the outcome, raise a message? When sampling w/ replacement could add a parameter to break once a certain fraction (potentially bigger than 1) of the population has been sampled; for now, take it to be 1.