[samples/pyhton] fix common {LINE->CV}_AA

```
$ python turing.py 

USAGE: turing.py [-o <output.avi>]

Press ESC to stop.

Traceback (most recent call last):
  File "turing.py", line 62, in <module>
    draw_str(vis, (20, 20), 'frame %d' % frame_i)
  File "/home/pkoch/sandbox/opencv/samples/python2/common.py", line 74, in draw_str
    cv2.putText(dst, s, (x+1, y+1), cv2.FONT_HERSHEY_PLAIN, 1.0, (0, 0, 0), thickness = 2, lineType=cv2.LINE_AA)
AttributeError: 'module' object has no attribute 'LINE_AA'
```
- http://docs.opencv.org/modules/core/doc/drawing_functions.html#line