Merge remote-tracking branch 'origin/2.4' into merge-2.4

Conflicts:
	modules/core/include/opencv2/core/types_c.h
	modules/gpu/src/cuda/imgproc.cu
	modules/gpu/src/cuda/safe_call.hpp
	modules/gpu/src/error.cpp
	modules/gpu/src/imgproc.cpp
	modules/imgproc/src/distransform.cpp
	modules/imgproc/src/shapedescr.cpp
	modules/python/src2/cv2.cpp
	modules/python/src2/cv2.cv.hpp

modules/features2d/src/bagofwords.cpp

@@ -147,7 +147,7 @@ void BOWImgDescriptorExtractor::compute( const Mat& image, std::vector<KeyPoint>
     int clusterCount = descriptorSize(); // = vocabulary.rows
 
     // Compute descriptors for the image.
-    Mat descriptors = _descriptors ? *_descriptors : Mat();
+    Mat descriptors;
     dextractor->compute( image, keypoints, descriptors );
 
     // Match keypoint descriptors to cluster center (to vocabulary)
@@ -176,6 +176,11 @@ void BOWImgDescriptorExtractor::compute( const Mat& image, std::vector<KeyPoint>
 
     // Normalize image descriptor.
     imgDescriptor /= descriptors.rows;
+	
+    // Add the descriptors of image keypoints
+    if (_descriptors) {
+        *_descriptors = descriptors.clone(); 
+    }
 }
 
 int BOWImgDescriptorExtractor::descriptorSize() const