I haven't had time to look through this PR yet (I've just been responding to comment), but I'm guessing that we'll have a few areas where the list of duplicated options will be needed. You could just have an array of options:

```js
// list out all duplicated options
var calendarOptions = [ "dateFormat", "min", "max", .. ];

// define widget
$.widget( "ui.datepicker", {
    options: {
        // only list unique options
        appendTo: null,
        ...
    },
    _setOption: function( key, value ) {
        // if key in calendarOptions, pass through
    }
});

// copy duplicated option defaults
$.each( calendarOptions, function( option ) {
    $.ui.datepicker.prototype.options[ option ] = $.ui.calendar.prototype.options[ option ];
});
```