PR# 5524 auto-completion in class/feature/cluster combo-boxes

In the class/feature/cluster combo-boxes, auto-completion only displays the first matching name. 75% of the time this is not the one that I want and auto-completion becomes useless in that case because I have to type the whole name anyway. In Rose Studio, when class/feature/cluster names are auto-completed in combo-boxes, it also displays the first matching name, but the other matching names can be traversed by using the up and down arrow keys. This functionality is very convenient and it would be great if we coud have it in EiffelStudio as well.

Note that I had a very hard time implementing this functionality because EV_COMBO_BOX is just rubbish. Pretending that it is a unique widget whereas there are in fact two widgets behind the scene causes a lot of troubles. I had to deal directly with the _IMP classes in order to make it work.