title: Python opencv feature detector causes segmentation fault
body: <p>I'm using Python 2.7 and opencv version 2.4.2. I'm having trouble with a segmentation fault. 
  Here is the code I try:</p>
  
  <pre><code>import cv2
  img = cv2.imread(img_path)
  img2 = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
  detector = cv2.FeatureDetector_create("SURF") # or "SIFT"
  kp  = detector.detect(img2)
  </code></pre>
  
  <p>the last line causes a segmentation fault and I don't understand why. I realize there is at least another post on the subject, namely : <a href="https://stackoverflow.com/questions/10799625/does-anyone-have-any-examples-of-using-opencv-with-python-for-descriptor-extract">Does anyone have any examples of using OpenCV with python for descriptor extraction?</a>
  but it doesn't seem to solve my problem. </p>
  
  <p>Any help will be much appreciated! Thanks!</p>