f2fs: add an option to avoid unnecessary BUG_ONs

If you want to remove unnecessary BUG_ONs, you can just turn off F2FS_CHECK_FS
in your kernel config.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

diff --cc fs/f2fs/checkpoint.c
Simple merge

diff --cc fs/f2fs/data.c
Simple merge

diff --cc fs/f2fs/dir.c
Simple merge

diff --cc fs/f2fs/f2fs.h
Simple merge

diff --cc fs/f2fs/file.c
Simple merge

diff --cc fs/f2fs/inode.c
Simple merge

diff --cc fs/f2fs/node.c
Simple merge

diff --cc fs/f2fs/recovery.c
Simple merge

diff --cc fs/f2fs/segment.c
Simple merge

diff --cc fs/f2fs/segment.h
Simple merge

diff --cc fs/f2fs/xattr.c
Simple merge