Backports compilation patches for ocaml-4.01.0beta1

I do know if there a policy over backport in opam-repository but here is two patches to fix the compilation of batteries and ocamlnet with 4.01.0beta1.

* patch for batteries is backport from [1]
* patch for ocamlnet is an adaptation of [2] has proposed in [3]

[1] https://github.com/ocaml-batteries-team/batteries-included/commit/1db918c5966c6f95dda9b2c4c26975b0a8fddb2c
[2] https://godirepo.camlcity.org/wwwsvn?rev=1790&root=lib-ocamlnet2&view=rev
[3] http://sourceforge.net/mailarchive/message.php?msg_id=31311878