added epsilon value to weights in the MergeMertens in order to avoid zero weights for pixels from uniformly filled areas of image

Conflicts:
	modules/cuda/test/test_objdetect.cpp
	modules/gpu/perf/perf_core.cpp
	modules/gpu/perf/perf_video.cpp
	modules/gpu/test/test_core.cpp

This is not meaningful when compiling to javascript, and causes warning
at linking stage.

Conflicts:
	modules/core/src/system.cpp

Conflicts:
	modules/ts/src/cuda_perf.cpp

Conflicts:
	cmake/OpenCVGenAndroidMK.cmake

Conflicts:
	modules/core/include/opencv2/core/version.hpp