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/os-specific/linux/s6-linux-utils/default.nix

@@ -2,7 +2,7 @@
 
 let
 
-  version = "2.0.2.3";
+  version = "2.2.0.0";
 
 in stdenv.mkDerivation rec {
 
@@ -10,12 +10,13 @@ in stdenv.mkDerivation rec {
 
   src = fetchurl {
     url = "http://www.skarnet.org/software/s6-linux-utils/${name}.tar.gz";
-    sha256 = "1hwc3dmqh4cyhx9b4gd48yvjrwmfkz968rncpqc511krpfwzyngr";
+    sha256 = "1y9mva7wk1ca2djq3qjh7hz756zk57yv7ljdnldn7k7jzfmlaxsq";
   };
 
   dontDisableStatic = true;
 
   configureFlags = [
+    "--enable-absolute-paths"
     "--includedir=\${prefix}/include"
     "--with-sysdeps=${skalibs}/lib/skalibs/sysdeps"
     "--with-include=${skalibs}/include"