we need a spec for handling mediums

[Mike Hearn]

> A dependency on a library is OK (as long as it's not too big), but
> dependencies on services are much more trouble. You can't really have the
> installation instructions for your software tell users to reconfigure
> their session manager to start a D-BUS session daemon before the software
> will run (especially on Windows, etc, but also on Linux).

Good point, it's too bad the only discovery mechanism is environment 
variables. Perhaps just have no notifications and a simplistic locking 
scheme if DBUS is missing (.... or allow DBUS installation, startup and 
discovery without leaving your session)