Create QDBusConnection after QApplication has been initialized

Doing otherwise causes Qt warning "QDBusConnection: session D-Bus
connection created before QCoreApplication. Application may misbehave."
Also, don't try to do anything D-Bus-related if connection fails.


git-svn-id: file:///data/workdir/Transmission-svn/trunk@14352 1bcf1a7e-6170-4b50-b784-84ec52b2dec6