[Sparkle] Update Badge

[Jack Small]

I've gotten a user request to badge the dock icon when an update is  
available, instead of showing the dialog suddenly, which he "hates".   
I pointed him to the checkbox in the preference pane that would stop  
the automatic update, naturally.  It ships turned off.

Still, the idea to use the dock badge seems like a really great idea.   
Maybe add a bounce to get their attention?  I'm not caught up with all  
the latest plans so if it's an old idea I'm sorry for the noise!

More later,
Jack