Add the loopback device, a device via which files can be accessed
as devices.
* conf/i386-pc.rmk (grub_emu_SOURCES): Add `disk/loopback.c'.
(pkgdata_MODULES): Add loopback.mod.
(loopback_mod_SOURCES): New variable.
(loopback_mod_CFLAGS): Likewise.
* conf/powerpc-ieee1275.rmk (grub_emu_SOURCES): Add
`disk/loopback.c'.
(pkgdata_MODULES): Add loopback.mod.
(loopback_mod_SOURCES): New variable.
(loopback_mod_CFLAGS): Likewise.
* disk/loopback.c: new file.
* include/grub/normal.h (grub_loop_init): New prototype.
(grub_loop_fini): New prototype.
* util/grub-emu.c (main): Initialize and de-initialize loopback
support.
* include/grub/disk.h (grub_disk_dev_id): Add
`GRUB_DISK_DEVICE_LOOPBACK_ID'.
