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: svn://svn.transmissionbt.com/Transmission/trunk@14352 f4695dd4-2c0a-0410-b89c-da849a56a58e