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/plane_tracker.py

@@ -21,6 +21,14 @@ Keys:
 Select a textured planar object to track by drawing a box with a mouse.
 '''
 
+# Python 2/3 compatibility
+from __future__ import print_function
+import sys
+PY3 = sys.version_info[0] == 3
+
+if PY3:
+    xrange = range
+
 import numpy as np
 import cv2
 
@@ -64,6 +72,7 @@ class PlaneTracker:
         self.detector = cv2.ORB_create( nfeatures = 1000 )
         self.matcher = cv2.FlannBasedMatcher(flann_params, {})  # bug : need to pass empty dict (#1329)
         self.targets = []
+        self.frame_points = []
 
     def add_target(self, image, rect, data=None):
         '''Add a new tracking target.'''
@@ -87,8 +96,8 @@ class PlaneTracker:
 
     def track(self, frame):
         '''Returns a list of detected TrackedTarget objects'''
-        frame_points, frame_descrs = self.detect_features(frame)
-        if len(frame_points) < MIN_MATCH_COUNT:
+        self.frame_points, frame_descrs = self.detect_features(frame)
+        if len(self.frame_points) < MIN_MATCH_COUNT:
             return []
         matches = self.matcher.knnMatch(frame_descrs, k = 2)
         matches = [m[0] for m in matches if len(m) == 2 and m[0].distance < m[1].distance * 0.75]
@@ -103,7 +112,7 @@ class PlaneTracker:
                 continue
             target = self.targets[imgIdx]
             p0 = [target.keypoints[m.trainIdx].pt for m in matches]
-            p1 = [frame_points[m.queryIdx].pt for m in matches]
+            p1 = [self.frame_points[m.queryIdx].pt for m in matches]
             p0, p1 = np.float32((p0, p1))
             H, status = cv2.findHomography(p0, p1, cv2.RANSAC, 3.0)
             status = status.ravel() != 0
@@ -169,7 +178,7 @@ class App:
                 break
 
 if __name__ == '__main__':
-    print __doc__
+    print(__doc__)
 
     import sys
     try: