update skarnet.org packages

execline:          2.1.4.5 -> 2.2.0.0
s6-dns:            2.0.0.7 -> 2.1.0.0
s6-linux-utils:    2.0.2.3 -> 2.2.0.0
s6-networking:     2.1.0.4 -> 2.2.1.0
s6-portable-utils: 2.1.0.0 -> 2.1.0.0 (no version change)
s6-rc:             0.0.2.1 -> 0.1.0.0
s6:                2.2.4.3 -> 2.4.0.0
skalibs:           2.3.9.0 -> 2.4.0.1

Also use new --enable-absolute-paths configure arg to correctly set
paths to runtime executables to point within the nix store rather than
relying on PATH resolution.

pkgs/tools/system/s6/default.nix

@@ -2,7 +2,7 @@
 
 let
 
-  version = "2.2.4.3";
+  version = "2.4.0.0";
 
 in stdenv.mkDerivation rec {
 
@@ -11,7 +11,7 @@ in stdenv.mkDerivation rec {
   src = fetchgit {
     url = "git://git.skarnet.org/s6";
     rev = "refs/tags/v${version}";
-    sha256 = "1jlavi3q6wmcxdcwsy42qcgfkl0ag6hwcgmi4g67dvqs9nqjq2a3";
+    sha256 = "0yf9apl05g1gxqwh01yd1iyg0xm50ywnlwp4szd08sg0srmvys16";
   };
 
   dontDisableStatic = true;
@@ -19,6 +19,7 @@ in stdenv.mkDerivation rec {
   enableParallelBuilding = true;
 
   configureFlags = [
+    "--enable-absolute-paths"
     "--with-sysdeps=${skalibs}/lib/skalibs/sysdeps"
     "--with-include=${skalibs}/include"
     "--with-include=${execline}/include"
@@ -30,11 +31,6 @@ in stdenv.mkDerivation rec {
   ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
   ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
-  preBuild = ''
-    substituteInPlace "src/daemontools-extras/s6-log.c" \
-      --replace '"execlineb"' '"${execline}/bin/execlineb"'
-  '';
-
   meta = {
     homepage = http://www.skarnet.org/software/s6/;
     description = "skarnet.org's small & secure supervision software suite";