Backported from X.org:

 commit a1cb69dc28fdbfbdfaf954e0bec221f759462399
 Author: Keith Packard <keithp@keithp.com>
 Date:   Fri Nov 15 22:05:44 2013 +0900

    Xext: Clean up warnings

    GC funcs and ops are const.
    Remove unused variables.
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

 Backport to nx-libs: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>