also add succeedOnFailure/keepBuildDirectory behaviour to source-tarball.nix

svn path=/nixpkgs/trunk/; revision=25400

pkgs/build-support/release/source-tarball.nix

@@ -68,6 +68,18 @@ stdenv.mkDerivation (
 
       eval "$postAutoconf"
     '';
+
+    failureHook = ''
+      if test -n "$succeedOnFailure"; then
+          if test -n "$keepBuildDirectory"; then
+              KEEPBUILDDIR="$out/`basename $TMPDIR`"
+              header "Copying build directory to $KEEPBUILDDIR"
+              ensureDir $KEEPBUILDDIR
+              cp -vR $TMPDIR/* $KEEPBUILDDIR
+              stopNest
+          fi
+      fi
+    '';
   }
 
   # Then, the caller-supplied attributes.