Attached patch allows PAE xenlinux to run in the shadow mode using

Attached patch allows PAE xenlinux to run in the shadow mode using
log-dirty guest-refcount, which is required to support
save/restore/relocate. We can turn on/off the mode every 5-sec interval
while doing kernel build (make -j4), for example, and it survives for
hours.

We are still restoring log-dirty mode for x86_64 xenlinux, which is not
very stable right now, but I believe it should be done very soon.

We also checked that it did not break 64-bit VMX domains, which uses
different sub-mode of the shadow mode.

Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Xiaohui Xin <xiaohui.xin@intel.com>