Python samples adapted for Python3 compatibility

Common fixes:
- print function
- int / float division
- map, zip iterators in py3 but lists in py2

Known bugs with opencv 3.0.0
- digits.py, called via digits_video.py: https://github.com/Itseez/opencv/issues/4969
- gaussian_mix.py: https://github.com/Itseez/opencv/pull/4232
- video_v4l2.py: https://github.com/Itseez/opencv/pull/5474

Not working:
- letter_recog.py due to changed ml_StatModel.train() signature

samples/python2/mouse_and_match.py

@@ -1,11 +1,13 @@
 #!/usr/bin/env python
 '''
-mouse_and_match.py [-i path | --input path: default ./]
+mouse_and_match.py [-i path | --input path: default ../data/]
 
 Demonstrate using a mouse to interact with an image:
  Read in the images in a directory one by one
  Allow the user to select parts of an image with a mouse
  When they let go of the mouse, it correlates (using matchTemplate) that patch with the image.
+
+ SPACE for next image
  ESC to exit
 '''
 
@@ -54,8 +56,10 @@ def onmouse(event, x, y, flags, param):
             drag_start = None
 
 if __name__ == '__main__':
+    print(__doc__)
+
     parser = argparse.ArgumentParser(description='Demonstrate mouse interaction with images')
-    parser.add_argument("-i","--input", default='./', help="Input directory.")
+    parser.add_argument("-i","--input", default='../data/', help="Input directory.")
     args = parser.parse_args()
     path = args.input
 
@@ -68,7 +72,7 @@ if __name__ == '__main__':
             print(infile)
 
             img=cv2.imread(infile,1)
-            if img == None:
+            if img is None:
                 continue
             sel = (0,0,0,0)
             drag_start = None