fix a bug: when the value changes from 1-31(>29/28) to 2-31

When I change the value from like 2013-1-31 to 2013-2-31(by scrolling the Month Column), the date picker's date(got by "date picker.date") will be 2013-3-3 and the day scroll view can't update to 28/29 rows(It's still 2013-2-31). But what I want is the day view can automatically update date rows to 28/29 according to whether the year is leap year if the previous day is larger than 28/29. So I try to fix this which is a bug for my case. I'm not clear what's your indent but I hope u can check the code I added. If u have more efficient way to solve my problem please tell me. 
Thanks for this project :D. And I'm sorry for my poor english....