title: Stemming some plurals with wordnet lemmatizer doesn't work
body: <p>Hi i've a problem with nltk (2.0.4):
  I'm trying to stemming the word 'men' or 'teeth' but it doesn't seem to work.
  Here's my code:</p>
  
  <pre><code>############################################################################
  import nltk
  from nltk.corpus import wordnet as wn
  from nltk.stem.wordnet import WordNetLemmatizer
  
  lmtzr=WordNetLemmatizer()
  words_raw = "men teeth"
  words = nltk.word_tokenize(words_raw)
  for word in words:
          print 'WordNet Lemmatizer NOUN: ' + lmtzr.lemmatize(word, wn.NOUN)
  #############################################################################
  </code></pre>
  
  <p>This should print 'man' and 'tooth' but instead it prints 'men' and 'teeth'.</p>
  
  <p>any solutions? </p>