[Libdlo] Equivalent for $DISPLAY

[Bernie Thompson]

It may take a few days to get to it, but I'd like to take Phil's
patch. It will mean find_first_device will disappear in favor of
claim_first_device.  If anyone has any counter-feedback (e.g. that
it'd be better to keep names same and just change implementation
underneath; or on the details of DLODISPLAY), please speak up shortly.

Thanks again for this patch, Phil!

Thanks,
Bernie