winXP "Standard PC" HAL and qemu-kvm >= 0.15

[Michael Tokarev <mjt@tls.msk.ru>]

As it turned out, a windowsXP machine does not work in
qemu-kvm >= 0.15 (it loses network and USB entirely)
if it is using "Standard PC" HAL.  In 0.14 it worked
fine, but not in 0.14 (I haven't tried any in-between
versions yet).

There are several HAL types available in winXP: these
are "Uniprocessor PC with MPS" (or Multiprocessor),
also two ACPI types, and "Standard PC".  All the other
HAL types appears to work fine, but not "Standard PC".

I haven't debugged further yet, -- because it were
not easy to find out what was causing the regression
and how to reproduce it, and also because I don't think
it is the right HAL for qemu-kvm guest anyway.

So, if anybody have some thoughts about this issue,
and especially if you know a way to switch winXP HAL
type to some ACPI variant without reinstalling, please
speak up.. ;)

Debian bugreport for a reference: http://bugs.debian.org/647312

Reproducer: install a winXP guest on kvm with -no-acpi so
it chooses an "Uniprocessor with MPS" HAL.  Switch it to
"Standard PC" in device manager, reboot -- in 0.15+ it does
not work anymore, while in 0.14 it continues to work fine.

Thank you!

/mjt