R: added wrapper script that provides "R" and "Rscript" binaries that know about extra libraries

Configure an override in ~/.nixpkgs/config.nix as follows:

  {
    packageOverrides = pkgs: {

      rWrapper = pkgs.rWrapper.override {
        packages = with pkgs.rPackages; [ Defaults dataTable foreach xtable ];
      };

    };
  }

pkgs/development/r-modules/generic/wrapper.nix

@@ -0,0 +1,18 @@
+{ stdenv, R, packages, makeWrapper }:
+
+stdenv.mkDerivation {
+  name = R.name + "-wrapper";
+
+  buildInputs = [makeWrapper R] ++ packages;
+
+  unpackPhase = ":";
+
+  installPhase = ''
+    mkdir -p $out/bin
+    cd ${R}/bin
+    for exe in *; do
+      makeWrapper ${R}/bin/$exe $out/bin/$exe \
+        --prefix "R_LIBS_SITE" ":" "$R_LIBS_SITE"
+    done
+  '';
+}

pkgs/top-level/all-packages.nix

@@ -6435,6 +6435,10 @@ let
     overrides = (config.rPackageOverrides or (p: {})) pkgs;
   });
 
+  rWrapper = callPackage ../development/r-modules/generic/wrapper.nix {
+    packages = [];
+  };
+
   ### SERVERS
 
   rdf4store = callPackage ../servers/http/4store { };