libgksu: fix sudo references (close #10524)

gksudo wasn't working because libgksu used wrong sudo file which doesn't have setuid bit

Committer: it isn't optimal, as it won't work on non-NixOS. I've got a
patch for it to use relative paths, but apparently something's wrong
with it and I don't want to kill much more time with it ATM.

pkgs/development/libraries/libgksu/default.nix

@@ -44,7 +44,7 @@ stdenv.mkDerivation rec {
 
     # Fix some binary paths
     sed -i -e 's|/usr/bin/xauth|${xauth}/bin/xauth|g' libgksu/gksu-run-helper.c libgksu/libgksu.c
-    sed -i -e 's|/usr/bin/sudo|${sudo}/bin/sudo|g' libgksu/libgksu.c
+    sed -i -e 's|/usr/bin/sudo|/var/setuid-wrappers/sudo|g' libgksu/libgksu.c
     sed -i -e 's|/bin/su\([^d]\)|/var/setuid-wrappers/su\1|g' libgksu/libgksu.c
 
     touch NEWS README