[libvirt] Minor fixes to ocaml bindings for storage pools/volumes

These patches fix a couple of minor issues I encountered while trying to manipulate storage pools and volumes from an OCaml program. If you're interested, the OCaml client code is a simple adapter to allow an XCP host to use libvirt (for storage only atm, more later). The client code (so far) is here: https://github.com/djs55/xcp-libvirt-storage/blob/master/server.ml Cheers, Dave Scott http://dave.recoil.org/