ceph: add feature bits to connection handshake (protocol change)

Define supported and required feature set.  Fail connection if the server
requires features we do not support (TAG_FEATURES), or if the server does
not support features we require.

Signed-off-by: Sage Weil <sage@newdream.net>

diff --cc fs/ceph/ceph_fs.h
Simple merge

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

diff --cc fs/ceph/messenger.c
Simple merge

diff --cc fs/ceph/msgr.h
Simple merge