xfrun and dbus

[Jani Monoses]

> xfrun4 should link with D-BUS, and use dbus-send as fallback. See
> exo_url_show() for details about how to invoke dbus-send so it reports
> success/failure (it's rather buggy).

I think it's simpler to just fallback to current dialog if calling dbus 
through the lib fails. I don't know why that would fail and dbus-send 
succeed, so in most cases will probably be extra overhead and making the
current dialog a fallback of a fallback :)

Jani