hexdump: do not segfault when iterating over an empty format string

Signed-off-by: Ondrej Oprala <ooprala@redhat.com>
libblkid: add support for btrfs backup superblock

Btrfs has three superblock. The first one is placed at 64KB, the second one at
64MB, the third one at 256GB.

If the first superblock is valid except that the "magic field" is zeroed, btrfs
skips the check of the other superblocks.  If the first superblock is fully
invalid, btrfs checks for the other superblock.

So zeroing the first superblock "magic field" at the beginning seems that the
filesystem is wiped. But when the first superblock is overwritten (eg by
another filesystem), then the other two superblock may be considered valid, and
the filesystem may resurrect.

This patch allow to find and wipe the other btrfs superblocks signature.

Signed-off-by: Karel Zak <kzak@redhat.com>
build-sys: add files to distribution

To fix 'make distcheck' compilation.  The fdisks/Makemodule.am has one
new entry 'dos_part_types.h', the rest is about sorting the list.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
build-sys: ignore chkdupexe

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
build-sys: cleanup --enable-most-builds list

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
libblkid: make btrfs magics more readable

Signed-off-by: Karel Zak <kzak@redhat.com>