Use the console mode automatically if no display can be found

[Calinou]

On a dedicated server, one usually does not have a display attached. If running the Quetoo updater without any arguments, it will crash due to a missing DISPLAY variable. (It can be made to run by passing -c, which enables the console mode.)

I suggest using the console mode automatically if no display can be found; this will make the user experience smoother for people setting up dedicated servers.

[jdolan]

Good call.