Increase <stop_date> and <nb_cow> to test computaion time and output file size

Suggested tests

Test			<stop_date>	<nb_cow>
 10cows- 10yr		1979-12-31	10
100cows- 10yr		1979-12-31	100
 10cows-100yr		2069-12-31	10
100cows-100yr		2069-12-31	100