vhd-tool, ocaml-vhd: Update to latest versions

Signed-off-by: Euan Harris <euan.harris@citrix.com>
xapi: Update to latest, removing use of stdext's Tar

Signed-off-by: Euan Harris <euan.harris@citrix.com>
mappkgname: Add ocaml-mirage-types and dependencies

Signed-off-by: Euan Harris <euan.harris@citrix.com>