Xen pygrub cannot handle grub2

[ezyang]

Xen needs this patch series ​​http://old-list-archives.xen.org/archives/html/xen-devel/2011-10/msg01404.html unfortunately they haven't been backported to Xen 4.0 or Xen 4.1 yet. (We specifically need only patches 2, 4 and 5). The pygrub executable patch is fuzzy, but easy to manually apply. Otherwise you won't be able to boot because the bootloader returns no data. Currently c-o has had its pygrub manually patched with these patches; we should talk to backports or package up these changes ourselves. The idea is to just install another pygrub, and then ask Xen to use it instead.