Add the Error exception and reorder the definitions of types
Add the Error exception and reorder the definitions of types

Unfortunately some of the field definitions mask each other,
so they need to be in the right order

Signed-off-by: Jon Ludlam <e7e3380887a8f95cc9dc4f0d51dedc7e849a287a@eu.citrix.com>

jonludlam/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs