Un-remove AutoComplete's ARIA live region.

AutoComplete accessibility improvements. Made the following changes based on advice from the Y! Accessibility team: - Removed role="combobox" from the input node. It's not appropriate for all AutoComplete use cases, and is usually not necessary. - Removes the live region that announces suggestions. It's redundant in assistive tools that properly support the other ARIA functionality that AutoComplete implements.

Switch to shim-plugin instead of widget-stack, and add a default z-index in the core autocomplete-list CSS. This fixes a shim bug in IE6 in which the shim wasn't sized correctly the first time the list was shown, and also resolves default z-index issues in all browsers that required implementers to manually set the z-index in JS in order for it to take effect.

Set list-style to none on both the list and the items.

Forgot to remove list styling. Oops.

ARIA improvements.

Create a new list node as a descendant of the content box. Previously, the content box itself was used as the list node, but this turns out to be inflexible since it prevents subclasses and implementers from adding additional display elements beyond the result list itself.

Add keyboard and mouse item selection and focus management.

Move autocomplete-list back under the autocomplete module. Make Y.AutoComplete an alias for Y.AutoCompleteList.