api : setEndDate and setStartDate BUG

[rwx666888]

step1:
$('#datetimepicker').datetimepicker('setEndDate', '2012-01-01');
step2:
$('#datetimepicker').datetimepicker('setEndDate', null);
now ,it can not to unset the limit. This limit is still '2012-01-01' , because line:533 this.endDate = endDate || this.endDate ('2012-01-01')