all-packages.nix: strip trailing whitespace
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 ];
      };

    };
  }
r-packages.nix: added various new libraries