title: cv2.CHAIN_APPROX_SIMPLE doesn't simplify the number of contour points for a rectangle
body: <p>I'm basically following <a href="https://opencv-python-tutroals.readthedocs.org/en/latest/py_tutorials/py_imgproc/py_contours/py_contours_begin/py_contours_begin.html" rel="nofollow">this python OpenCV contour guide</a>.
  I'm using <code>OpenCV 2.4.11</code> installed through <code>Brew</code> (OSX).</p>
  
  <p>Everything appears to basically work, other than when I do:
  <code>contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)</code></p>
  
  <p>I get the same number of contour coordinate points as with <code>cv2.CHAIN_APPROX_NONE</code>.</p>
  
  <p>So in the example of the link, I still get <code>734</code> points rather than <code>4</code>.</p>
  
  <p>Anyone else experienced this?</p>
  
  <p>NB: (Note that <code>cv2.findContours</code> returns <code>contours, hierarchy</code> contrary to the documentation).</p>