Unionfs: imported fixes from korg branch

Unionfs: imported fixes from korg branch

Export release_open_intent.
SElinux: xattr fixes (CAP_FOWNER).
unionfs_xattr_kfree inline function.
alloc_lower_nd -> init_lower_nd.
free_lower_nd -> release_lower_nd.
unionfs_purge_extras -> unionfs_postcopyup_release.
unionfs_inherit_mnt -> unionfs_postcopyup_setmnt.
minor code/copyright cleanups.
MS_SILENT remount fix.
simplify unionfs_mntget/put.

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