pygrub regression with latest xen-unstable test

[Fabio Fantoni <fabio.fantoni@m2r.biz>]

After updating to latest xen-unstable (commit 
7d203b337fb2dcd148d2df850e25b67c792d4d0b) I'm unable to boot an old domU 
with grub 1 cfg.
I not remember the previous unstable build tested that successfull boot 
it, probably is of 1-2 months ago or more.

#boot/grub/menu.lst
title Lenny 2.6.26
root (hd0,0)
kernel /boot/vmlinuz-2.6.26-2-xen-amd64 ro root=/dev/xvda1 console=hvc0 
xencons=tty
initrd /boot/initrd.img-2.6.26-2-xen-amd64

xl create /etc/xen/nagios.cfg
Parsing config from /etc/xen/nagios.cfg
libxl: error: libxl_bootloader.c:630:bootloader_finished: bootloader 
failed - consult logfile /var/log/xen/bootloader.11.log
libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: bootloader 
[-1] exited with error status 1
libxl: error: libxl_create.c:1133:domcreate_rebuild_done: cannot 
(re-)build domain: -3

#/var/log/xen/bootloader.11.log
Using <class 'grub.GrubConf.GrubConfigFile'> to parse /boot/grub/menu.lst
ESC(BESC)0ESC[1;24rESC[m^OESC[?7hESC[?1hESC=ESC[?1lESC>ESC[24;1H^MESC[?1lESC>Traceback 
(most recent call last):
   File "/usr/lib/xen/bin/pygrub", line 894, in <module>
     raise RuntimeError, "Unable to find partition containing kernel"
RuntimeError: Unable to find partition containing kernel

If you need more information and/or tests tell me and I'll post them.

Thanks for any reply.