Add support for Xen PVH guest types introduced in Xen 4.4.  Without
the patch, running against a Xen 4.4 hypervisor binary would fail
during session initialization with the error message "crash: invalid
structure member offset: domain_is_hvm".  In addition, the PVH guest
type is being registered internally as an HVM guest type, the debug
"help -X ofs" command's display of the domain_domain_flags offset
has been fixed to show it in decimal, and the setting of the internal
dc->domain_flags has been fixed to contain all flags set, not just
the first one found.
(dslutz@verizon.com)