commit bc348bd2c42f3f18786085ccef2f010eff5bf3d2
 Author: Jon TURNEY <jon.turney@dronecode.org.uk>
 Date:   Mon Mar 11 14:34:32 2013 +0000

    Handle -displayfd and an explicit display number sensibly

    Handle -displayfd and an explicit display number sensibly, e.g. use the
    explicitly specified display number, and write it to the displayfd

    v2: displayfd might be 0, so use -1 as invalid value
    v3: Rebase for addition of NoListenAll flag
Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Backported-to-NX-by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>