If negative entries (nodeid == 0) were sent in reply to LOOKUP requests,
two bugs could be triggered:

- looking up a negative entry would return -EIO,

- revaildate on an entry which turned negative would send a FORGET
  request with zero nodeid, which would cause an abort() in the
  library.

The above would only happen if the 'negative_timeout=N' option was used,
otherwise lookups reply -ENOENT, which worked correctly.
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>