Use a GNU tar flag to shut up warnings about implausibly old timestamp

corepkgs/config.nix.in

@@ -9,6 +9,7 @@ in {
   bzip2 = "@bzip2@";
   xz = "@xz@";
   tar = "@tar@";
+  tarFlags = "@tarFlags@";
   tr = "@tr@";
   curl = "@curl@";
   nixBinDir = fromEnv "NIX_BIN_DIR" "@bindir@";

corepkgs/unpack-channel.nix

@@ -6,7 +6,7 @@ let
     ''
       mkdir $out
       cd $out
-      ${bzip2} -d < $src | ${tar} xf -
+      ${bzip2} -d < $src | ${tar} xf - --warning=no-timestamp 
       mv * $out/$channelName
     '';