Avoid QDBusConnection Qt warning message for each KUniqueApplication

[Allen Winter]

On Saturday, November 17, 2012 10:55:01 AM David Faure wrote:
> 
> I know that I said "not a problem in KF5 anymore", but kdelibs4 is still going 
> to be used for a very long time, and warnings on startup don't make it appear 
> very polished... Could you take a look at it -- based on the current code 
> rather than a theoretical idea of how it should work? :-)
> 

Another reason to fix this is so we can use QT_FATAL_WARNINGS effectively
on Qt4 based apps.

As it it now, setting QT_FATAL_WARNINGS makes the app die immediately
on those QDBusConnection warnings.

So +1 on getting this fixed