Backport of X.org commit:

 commit 2d93e69690d2c5d4a89a795ede6423796528e5df
 Author: Alan Coopersmith <alan.coopersmith@sun.com>
 Date:   Thu Sep 27 16:47:06 2007 -0700

    Rework local client id finding code to be more uniform
Backported-to-NX-by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>

 Note: This commit also switches client_uid_string's size from 32 to 64 chars,
 as found in this X.org commit (spotted by Mihai Moldovan during code review):

    commit a7b944f0d96c3e0e15e75378a04def1ac96089fb
    Author: Alan Coopersmith <alan.coopersmith@sun.com>
    Date:   Wed Nov 1 16:17:49 2006 -0800

        If getpeerucred() is available, include pid & zoneid in audit messages too