DatePicker _selectDate doesn't have to use $(id)

[Debbus]

In DatePicker in the function '_selectDay' and '_selectDate' (there are more) the first thing what is done, is that via $(id) a target is retrieved from the DOM.

      _selectDay: function (id, month, year, td) {
         var target = $(id);

However, you shouldn't have to do this, because the current instance is known.

      _selectDay: function (id, month, year, td) {
         var target = this._curInst.input;

[utkarsh]

This change breaks 5 unit tests on DatePicker (All involving inline date picker + mouse).

[Scott González]

Datepicker is going to be rewritten. The rewrite will follow our normal coding standards and use the widget factory, which will avoid this problem.