Update datePicker.js

Correct "month-mode"+"Sunday-first mode" calender display, when the 1st of the month falls on a Sunday. Fixes #119.
Update datePicker.js
Update datePicker.js
Update datePicker.js
Update datePicker.js

OK, it may not be pretty, but I think I got it working at last.
Merge pull request #120 from garfield69/patch-2

Update datePicker.js