cmdliner-devel should be ocaml-cmdliner-devel

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Resync ocaml-vhd with xenserver/buildroot

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #61 from djs55/nbd

Resync cmdliner, ocaml-vhd with xenserver/buildroot