emulators/virtualbox-ose: fix make config annoyance

[Beat Gaetzi]

Hi,

barbara wrote:
> Running make config on emulators/virtualbox-ose-additions will cause the settings for emulators/virtualbox-ose and vice-versa.

We will add a CONFLICT between emulators/virtualbox-ose-additions and
emulators/virtualbox-ose with the next port update, because there is no
need to install them on the same machine. On the host you install
emulators/virtualbox-ose and emulators/virtualbox-ose-additions is only
for FreeBSD guests. We have some reports that installing and running
both ports on the same machine may cause system instabilities.

Beat