Combobox example expanded to make interaction more like other comboboxes

[BigBlueHat]

I've added a few features to the combobox code example given in the documentation: ​http://jqueryui.com/demos/autocomplete/#combobox

The additions include:1

1. selection of single remaining item if tab or enter is pressed
2. selection of an available option is "forced"

-- unlike autocomplete, choices should be restricted to the available list of options in a combobox

NOTE: #2 could be debated (or made configurable) if the combobx was being used for creation *or* selection vs. just selection.

The full ui.combobox is avaiable here: ​https://gist.github.com/929478

[Scott González]

The combobox is just a demo, it's not a full widget. Unless it becomes a fully designed, documented and tested widget, we don't want to add features or options or change any behavior unless something is clearly broken.

[BigBlueHat]

Why not continue to iterate on it in the wiki, so it could be considered a full-fledged widget later? There are no doubt people (like me) who are using it in production and would appreciate knowing it was still being cared for in some way.

Please consider adding this to the Demos & Documentations section and/or giving the community a way to contribute to those demos.

Thanks.