The new sample adjust some parameters thus it should always be able to
calculate valid homography matrix when input is box.png and
box_in_scene.png.
Pure cpp surf and bfmatcher implementation is also added to show the user
its accuracy and performance.

A modification of the JavaCameraView is needed to avoid a crash when the
app is exited. It is a good practice to remove the callback after the
stopPreview method.

Also, removed the one from modules/python/src2/cv.py and cleared its
executable bit, since it's not a script.

replaced wrong check to correct check