commit 88bacc49f06da5927f716869f5a32672a8297ed0
 Author: Chase Douglas <chase.douglas@canonical.com>
 Date:   Wed Apr 4 15:29:42 2012 -0700

    os: Add -displayfd option

    This option specifies a file descriptor in the launching process.  X
    will scan for an available display number and write that number back to
    the launching process, at the same time as SIGUSR1 generation.  This
    means display managers don't need to guess at available display numbers.
    As a consequence, if X fails to start when using -displayfd, it's not
    because the display was in use, so there's no point in retrying the X
    launch on a higher display number.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Reviewed-by: Julien Cristau <jcristau@debian.org>
Tested-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Backported-to-NX-by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>