even more important testing by Colin.
* Makefile.util.def (libgrubmods.a): Add crc.c and gzio.c
* grub-core/Makefile.core.def (btrfs): Add crc.c.
* grub-core/fs/btrfs.c: Stub replaced with real implementation.
* grub-core/io/gzio.c (grub_gzio): New fields mem_input_size,
mem_input_off and mem_input. All users updated to accept in-RAM input.
(gzio_seek): New function.
(test_zlib_header): Likewise.
(grub_gzio_read): Likewise.
(grub_zlib_decompress): Likewise.
* grub-core/kern/emu/getroot.c (grub_find_root_device_from_mountinfo):
Accept partial and non-virtual mounts.
(grub_guess_root_device): Do rescanning after device_from_mountinfo to
avoid receiving /dev/dm-X as device.
* grub-core/kern/emu/misc.c (grub_make_system_path_relative_to_its_root):
Handle bind and partial mounts.
* grub-core/lib/crc.c: New file.
* include/grub/deflate.h: Likewise.
* include/grub/emu/misc.h (grub_find_root_device_from_mountinfo): New
proto.
* include/grub/lib/crc.h: New file.
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