Unionfs: handle whiteouts more efficiently in filldir

Unionfs: handle whiteouts more efficiently in filldir

If we cache a dirent for file "foo", and then it gets deleted, then we look
for a ".wh.foo" whiteout entry in the same dirent cache.  But our dirent
cache strips the ".wh." prefix, thus looking for an entry named "foo" whose
filldir_node->whiteout should be 1 instead of 0.  In that case, don't
display  an incorrect printk  message that the file system may be corrupt,
but set that filldir_node->whiteout to 1.

CC: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>