[widgets] TWI: Fixes to test cases

Hi everyone,

Just a quick heads up that I've checked in some fixes to bugs in the  
Widget Interface test cases in CVS.

I also noticed an issue with the WebIDL test case that I wasn't  
willing to dive into as I believe it is auto-generated from the  
documentation (?) - this is a misinterpretation of the "WindowWidget"  
abstract interface; the test checks for a "WindowWidget" interface  
even though the spec doesn't require one - it just requires the window  
interface to have a widget object.

S