[CVE-2013-0190] xen: Fix stack corruption in xen_failsafe_callback for 32bit PVOPS guests

[Luis Henriques]

Following this email there are 3 patches that fix this vulnerability for
Lucid, Precise and Quantal.  These fixes have been prepared by Stephan
and are Ack'ed by me.

Note that the Precise and Quantal fixes are already in upstream stable
trees and would probably have been included in the next SRU cycle anyway.

Cheers,
--
Luis