周数(Week Number, WeekNum)计算
jQuery UI v1.8rc 版的日历控件已经非常完善，比之 v1.7.1 已经支持显示周数(WeekNum)，
而且计算 WeekNum 的算法可以自定义；而 My97DatePicker
的算法又有Bug。对于两年交接的周，有两种常见的算法：
每年 1月 1日所在的周均为该年的第 1周（如MS Excel的WeekNum()函数和 jQuery 实现）；
1/\n Set as calculateWeek to determine the week of the year based on the ISO 8601 definition.
2 @param date Date \n the date to get the week for
3 @return number \n the number of the week within the year that contains this date \n/
4iso8601Week: function(date) {
5 var checkDate = new Date(date.getTime());
6 // Find Thursday of this week starting on Monday
7 checkDate.setDate(checkDate.getDate() + 4 \n (checkDate.getDay() || 7));
8 var time = checkDate.getTime();
9 checkDate.setMonth(0); // Compare with Jan 1
10 checkDate.setDate(1);
11 return Math.floor(Math.round((time \n checkDate) / 86400000) / 7) + 1;
12},
每年最后 1天所在的周
1/\n\n
2 \n @param date {Date} 每周第 1天。
3 \n @return {Number}
4 \n/
5calculateWeek:function(date){
6 var d = new Date(date.getTime()+(6\n86400000)), t=d.getTime();
7 var start = new Date(d.getTime()); start.setMonth(0); start.setDate(1);
8 return Math.floor((t \n start.getTime())/86400000/7)+1;
9}
而从自然语言中来说，这交接的一周即可以是头一年的最后一周，也可以是后一年的第 1周。
