[REVIEW REQUEST] Add support for an emptyText property in ComboBox

[Jonathan Giles]

Hi all,

http://javafx-jira.kenai.com/browse/RT-22972

I'm keen to add an 'emptyText' property to ComboBox. This property would 
be analogous to the 'promptText' property already supported, except that 
it would appear in the popup list area when the items list is empty 
(rather than in the text field when that is empty).

I'm happy to accept alternate naming suggestions, as this is just the 
first name that occurred to me.

-- 
-- Jonathan