dbus-python seems to be not thread safe. After "881ee76 Merge qclipd
into qubes-manager" this occasionally triggers SEGV.
QtDBus seems to be somehow less robust:
- doesn't automatically convert methods arguments to proper types based
on introspection data
- property access isn't working so must call
org.freedesktop.DBus.Properties methods manually
But besides those problems seems to work stable.