Unionfs: port to 3.13-rc1

Unionfs: port to 3.13-rc1

Use file_inode helper.

Add NULL extra arg to vfs_* methods and notify_change where it takes a
delegated inode.

Check DCACHE_OP_REVALIDATE flag in ->d_revalidate.

->setattr implemented, but not used yet.

Force our root dentry to be of type DIR.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>