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/video_v4l2.py

@@ -14,6 +14,9 @@ Keys:
 
 '''
 
+# Python 2/3 compatibility
+from __future__ import print_function
+
 import cv2
 
 def decode_fourcc(v):
@@ -24,13 +27,13 @@ font = cv2.FONT_HERSHEY_SIMPLEX
 color = (0, 255, 0)
 
 cap = cv2.VideoCapture(0)
-cap.set(cv2.CAP_PROP_AUTOFOCUS, False)
+cap.set(cv2.CAP_PROP_AUTOFOCUS, False)  # Known bug: https://github.com/Itseez/opencv/pull/5474
 
 cv2.namedWindow("Video")
 
 convert_rgb = True
 fps = int(cap.get(cv2.CAP_PROP_FPS))
-focus = int(cap.get(cv2.CAP_PROP_FOCUS)) * 100
+focus = int(min(cap.get(cv2.CAP_PROP_FOCUS) * 100, 2**31-1))  # ceil focus to C_LONG as Python3 int can go to +inf
 
 cv2.createTrackbar("FPS", "Video", fps, 30, lambda v: cap.set(cv2.CAP_PROP_FPS, v))
 cv2.createTrackbar("Focus", "Video", focus, 100, lambda v: cap.set(cv2.CAP_PROP_FOCUS, v / 100))
@@ -55,7 +58,7 @@ while True:
     cv2.putText(img, "FPS: {}".format(fps), (15, 80), font, 1.0, color)
     cv2.imshow("Video", img)
 
-    k = cv2.waitKey(1)
+    k = 0xFF & cv2.waitKey(1)
 
     if k == 27:
         break