title: sklearn plot confusion matrix with labels
body: <p>I want to plot a confusion matrix to visualize the classifer's performance, but it shows only the numbers of the labels, not the labels themselves:</p>
  
  <pre><code>from sklearn.metrics import confusion_matrix
  import pylab as pl
  y_test=['business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business', 'business']
  
  pred=array(['health', 'business', 'business', 'business', 'business',
         'business', 'health', 'health', 'business', 'business', 'business',
         'business', 'business', 'business', 'business', 'business',
         'health', 'health', 'business', 'health'], 
        dtype='|S8')
  
  cm = confusion_matrix(y_test, pred)
  pl.matshow(cm)
  pl.title('Confusion matrix of the classifier')
  pl.colorbar()
  pl.show()
  </code></pre>
  
  <p>How can I add the labels (health, business..etc) to the confusion matrix?</p>