title: NLTK stem words produces odd results
body: <p>After running <code>nltk.stem.porter.PorterStemmer().stem_word(word)</code> I get many words with 'ing' cut off or 'y' swapped with 'i' . e.g. 'Quality' becomes 'Qualiti' and (even stranger) 'value' becomes 'valu'?</p>
  
  <p>As the resulting words are not actual english words, I am not sure how am I meant to use them? My best guess is that I am meant to put the stem words into another function which will give me all the derived/child words from this stem (e.g. 'valu' would return <code>['valuing','valued', 'values', ...]</code>. Is there such a function?</p>