e2fsck: add support for dir_data feature

e2fsck: add support for dir_data feature

Add support for the INCOMPAT_DIRDATA feature, which allows
storing extra data in the directory entry beyond the name.
This allows the Lustre File IDentifier to be accessed in
an efficient manner, and would be useful for expanding a
filesystem to allow more than 2^32 inodes in the future.

  LU-1774 e2fsck: e2fsck -D does not change dirdata content

  Fix dir optimization to preserver dirdata content for dot
  and dotdot entries.

  Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
  Change-Id: Iae190794da75a2080a8e5cc5b95a49e0c894f72f

Signed-off-by: Pravin Shelar <pravin@clusterfs.com>
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>