fixed find_obj.py

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

    Update find_obj.py:
    Added additional error checking for the loaded files and modified the detector check to be more pythonic (is versus ==).

    Update common.py:
    Fixed a typo (contais -> contains)

ASIFT

small fix in find_obj.py

- handle bad matching case
- use BFMatcher and FlannBasedMatcher (and thus fixing a bug: L2^2 metric was used for flann)

fixed "import cv" in the new python samples. corrected Python bindings to match the documentation and vice versa (NOTE: in cv2.stereoCalibrate the parameter ordering has been changed)