Fix for the support of compressed kdump clones created with the KVM
"virsh dump --memory-only --format <compression-type>" command,
where the compression-type is either "kdump-zlib", "kdump-lzo" or
"kdump-snappy".  Without the patch, if an x86_64 guest kernel was loaded
with a non-zero "phys_base", the "--machdep phys_base=<offset>" command
line option was required as a workaround or the crash session would fail
with the warning message "WARNING: cannot read linux_banner string"
followed by the fatal error message "crash: vmlinux and <dumpfile name>
do not match!".
(anderson@redhat.com)