NSCalendar method to floor date to some calendar unit

NSCalendar+QS.m

- (NSDate *) floorDate: (NSDate *) inDate
  toCalendarUnit: (NSInteger) inCalendarUnit
{
	NSDateComponents	*dateComponents;
	NSInteger			calendarUnits = 0;
	
	switch (inCalendarUnit) {
		case NSSecondCalendarUnit:	calendarUnits |= NSSecondCalendarUnit;
		case NSMinuteCalendarUnit:	calendarUnits |= NSMinuteCalendarUnit;
		case NSHourCalendarUnit:	calendarUnits |= NSHourCalendarUnit;
		case NSDayCalendarUnit:		calendarUnits |= NSDayCalendarUnit;
		case NSMonthCalendarUnit:	calendarUnits |= NSMonthCalendarUnit;
		case NSYearCalendarUnit:	calendarUnits |= NSYearCalendarUnit;
	}
	
	if (calendarUnits) {
		dateComponents = [self components: calendarUnits fromDate: inDate];
		inDate = [self dateFromComponents: dateComponents];
	}
	
	return inDate;
}