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

Conflicts:
	modules/core/src/gl_core_3_1.cpp
	modules/core/src/opencl/convert.cl
	modules/cudaimgproc/src/cuda/canny.cu
	modules/cudastereo/perf/perf_stereo.cpp
	modules/gpu/perf/perf_imgproc.cpp
	modules/gpu/test/test_denoising.cpp
	modules/ocl/src/opencl/imgproc_resize.cl
	samples/cpp/Qt_sample/main.cpp

modules/java/generator/src/java/core+TermCriteria.java

@@ -87,7 +87,6 @@ public class TermCriteria {
 
     @Override
     public String toString() {
-        if (this == null) return "null";
         return "{ type: " + type + ", maxCount: " + maxCount + ", epsilon: " + epsilon + "}";
     }
 }