opencv: Fix iSight camera capture for OpenCV 2.4.6.1.

In OpenCV 2.4.6.1 several webcams (including iSight) fails to capture frames unless you do some magic with cv2.namedWindow and cv2.waitKey applied.
Fortunately the guys from MacPorts faced with the same problem and found the solution earlier: https://trac.macports.org/browser/trunk/dports/graphics/opencv/files/patch-issue-3156.diff.
I created independent diff at https://gist.github.com/Sitin/7172726.