btrfs-progs: force overwrite should wipe stale SB

Here is a test case which says it all..

mkfs.xfs -f $DEV
mkfs.btrfs -f $DEV
mount $DEV $MNT
mount: /dev/vdiskc: more filesystems detected. This should not happen,
       use -t <type> to explicitly specify the filesystem type or
       use wipefs(8) to clean up the device.

mount: you must specify the filesystem type

with this patch btrfs_prepare_device() also wipes old FS if any,
btrfs_prepare_device() is called after we have verified that
user has provided -f option.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: fix many typos in documents

There are many trivial typos in Documentation/*.txt.
All of these use "exist status" to mean "exit status"
by mistake. I guess someone first made this mistake
and it has spread by copy-and-paste :-D

Signed-off-by: Naohiro Aota <naota@elisp.net>
Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: Properly cast to avoid compiler warnings, fixes FTBFS on alpha and ia64

Bug-Debian: http://bugs.debian.org/539433
Bug-Debian: http://bugs.debian.org/583768
Authors:
 Luca Bruno <lucab@debian.org>
 Alexander Kurtz <kurtz.alex@googlemail.com>
 Daniel Baumann <daniel.baumann@progress-technologies.net>

Signed-off-by: Dimitri John Ledkov <xnox@debian.org>
Signed-off-by: David Sterba <dsterba@suse.cz>