nilfs2: reject incompatible filesystem

This forces nilfs to check compatibility of feature flags so as to
reject a filesystem with unknown features when it mounts or remounts
the filesystem.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

diff --cc fs/nilfs2/nilfs.h
Simple merge

diff --cc fs/nilfs2/super.c
Simple merge

diff --cc fs/nilfs2/the_nilfs.c
Simple merge