Screen versus CRTC hint

Yet another pull request that continues the DRM branch. This
commit (last commit the list below) continues pull request #44,
and gives a helpful hint if the user tries set screen to higher
that 0 if there is only one screen.

If only screen 0 exists and the user tries to select, for example,
screen 1, it will suggest selecting CRTC 1. And if this is done
when vidmode is selected it will also suggest randr.