Minor modifications of some ocaml packages:

adds myself as a maintainer
adds assertions to have evaluation errors rather than build errors
moves opam out of ocamlPackages, as it does not provide a library

pkgs/development/ocaml-modules/extlib/default.nix

@@ -1,5 +1,7 @@
 {stdenv, fetchurl, ocaml, findlib, minimal ? true}:
 
+assert stdenv.lib.versionAtLeast (stdenv.lib.getVersion ocaml) "3.11";
+
 stdenv.mkDerivation {
   name = "ocaml-extlib-1.6.1";