netrw: Allow to specify checksum hash library.

Within netrw the only checksum algorithm that is available is MD5. We thus make
it possible for users to override this, so algorithms from other libraries such
as OpenSSL and MHash can used.

pkgs/tools/networking/netrw/default.nix

@@ -1,9 +1,23 @@
-{ stdenv, fetchurl }:
+{ stdenv, fetchurl
+, checksumType ? "built-in"
+, libmhash ? null
+, openssl ? null
+}:
+
+assert checksumType == "mhash" -> libmhash != null;
+assert checksumType == "openssl" -> openssl != null;
 
 stdenv.mkDerivation rec {
   name = "netrw-${version}";
   version = "1.3.2";
 
+  configureFlags = [
+    "--with-checksum=${checksumType}"
+  ];
+
+  buildInputs = stdenv.lib.optional (checksumType == "mhash") libmhash
+             ++ stdenv.lib.optional (checksumType == "openssl") openssl;
+
   src = fetchurl {
     urls = [
       "http://mamuti.net/files/netrw/netrw-${version}.tar.bz2"