BugFix#1636; fix the issue where the user could add any birthday for his contact.

There is still one case that are not handle on the verification;
1- It does not check if the date is real, for instance 31 february is possible with the current code.

I would suggest implementing a graphic calendar where the user could pick a date with a single click.
something like this : http://calendarview.org/ or like this http://jsfiddle.net/JvTTa/