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

Conflicts:
	cmake/OpenCVModule.cmake
	doc/tutorials/calib3d/camera_calibration/camera_calibration.rst
	doc/tutorials/features2d/feature_detection/feature_detection.rst
	doc/tutorials/features2d/feature_flann_matcher/feature_flann_matcher.rst
	doc/tutorials/features2d/feature_homography/feature_homography.rst
	modules/core/include/opencv2/core/operations.hpp
	modules/core/src/arithm.cpp
	modules/gpu/perf/perf_video.cpp
	modules/imgproc/include/opencv2/imgproc/imgproc.hpp
	modules/java/generator/gen_java.py
	modules/java/generator/src/cpp/VideoCapture.cpp
	modules/nonfree/src/opencl/surf.cl
	modules/ocl/include/opencv2/ocl/ocl.hpp
	modules/ocl/perf/perf_haar.cpp
	modules/ocl/perf/perf_precomp.hpp
	modules/ocl/src/color.cpp
	modules/ocl/src/filtering.cpp
	modules/ocl/test/test_color.cpp
	modules/ocl/test/test_objdetect.cpp
	modules/python/src2/cv2.cpp
	samples/gpu/CMakeLists.txt
	samples/gpu/super_resolution.cpp

modules/imgproc/src/pyramids.cpp

@@ -191,6 +191,7 @@ pyrDown_( const Mat& _src, Mat& _dst, int borderType )
     typedef typename CastOp::type1 WT;
     typedef typename CastOp::rtype T;
 
+    CV_Assert( !_src.empty() );
     Size ssize = _src.size(), dsize = _dst.size();
     int cn = _src.channels();
     int bufstep = (int)alignSize(dsize.width*cn, 16);