* disk/lvm.c (grub_lvm_scan_device): Allocate buffer space for the
circular metadata worst case scenario. If the metadata is circular
then copy the wrap in place.
* include/grub/lvm.h: Add GRUB_LVM_MDA_HEADER_SIZE, from the LVM2
project lib/format_text/layout.h
Circular metadata bug found and patch debugged by Jan Derk Gerlings.